<?xml version="1.0" encoding="US-ASCII"?>
<!-- DFIN New ActiveDisclosure (SM) XBRL Linkbase Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date :2023-02-17T15:46:58.8344+00:00 -->
<!-- Copyright (c) 2023 Donnelly Financial Solutions, Inc. All Rights Reserved. -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedBalanceSheet1" xlink:href="ck0001925309-20221231.xsd#StatementConsolidatedBalanceSheet1" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedBalanceSheetParenthetical" xlink:href="ck0001925309-20221231.xsd#StatementConsolidatedBalanceSheetParenthetical" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedStatementOfOperations" xlink:href="ck0001925309-20221231.xsd#StatementConsolidatedStatementOfOperations" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedScheduleOfInvestments1" xlink:href="ck0001925309-20221231.xsd#StatementConsolidatedScheduleOfInvestments1" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedScheduleOfInvestmentsParenthetical" xlink:href="ck0001925309-20221231.xsd#StatementConsolidatedScheduleOfInvestmentsParenthetical" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedStatementsOfChangesInNetAssets" xlink:href="ck0001925309-20221231.xsd#StatementConsolidatedStatementsOfChangesInNetAssets" xlink:type="simple"/>
  <link:roleRef roleURI="http://xbrl.sec.gov/cef/role/RiskOnly" xlink:href="https://xbrl.sec.gov/cef/2022/cef-2022.xsd#RiskOnly" xlink:type="simple"/>
  <link:roleRef roleURI="http://xbrl.sec.gov/cef/role/SecurityOnly" xlink:href="https://xbrl.sec.gov/cef/2022/cef-2022.xsd#SecurityOnly" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureSignificantAccountingPoliciesAdditionalInformationDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureSignificantAccountingPoliciesAdditionalInformationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureAgreementsAndRelatedPartyTransactionsAdditionalInformationDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureAgreementsAndRelatedPartyTransactionsAdditionalInformationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureInvestmentsAtFairValueAdditionalInformationDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureInvestmentsAtFairValueAdditionalInformationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureInvestmentsAtFairValueSummaryOfInvestmentsAtFairValueDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureInvestmentsAtFairValueSummaryOfInvestmentsAtFairValueDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureInvestmentsAtFairValueSummaryOfIndustryCompositionOfInvestmentsAtFairValueDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureInvestmentsAtFairValueSummaryOfIndustryCompositionOfInvestmentsAtFairValueDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureInvestmentsAtFairValueSummaryOfGeographicCompositionOfInvestmentsAtFairValueDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureInvestmentsAtFairValueSummaryOfGeographicCompositionOfInvestmentsAtFairValueDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDerivativesSummaryOfAmountsPaidAndReceivedOnInterestRateSwapTransactionsExcludingUpfrontFeesDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureDerivativesSummaryOfAmountsPaidAndReceivedOnInterestRateSwapTransactionsExcludingUpfrontFeesDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDerivativesAdditionalInformationDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureDerivativesAdditionalInformationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsFairValueMeasurementsOfInvestmentsDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureFairValueOfFinancialInstrumentsFairValueMeasurementsOfInvestmentsDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsChangesInFairValueOfInvestmentsUsingLevel3InputsDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureFairValueOfFinancialInstrumentsChangesInFairValueOfInvestmentsUsingLevel3InputsDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsNetChangeInUnrealizedGainsOrLossesOnInvestmentsForWhichLevel3InputsWereUsedInDeterminingFairValueDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureFairValueOfFinancialInstrumentsNetChangeInUnrealizedGainsOrLossesOnInvestmentsForWhichLevel3InputsWereUsedInDeterminingFairValueDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsFairValueOfLevel3InvestmentsAtFairValueSignificantUnobservableInputsUsedInValuationsDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureFairValueOfFinancialInstrumentsFairValueOfLevel3InvestmentsAtFairValueSignificantUnobservableInputsUsedInValuationsDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsFairValueOfFinancialInstrumentsFairValueOfNotesDetails" xlink:href="ck0001925309-20221231.xsd#DisclosureFairValueOfFinancialInstrumentsFairValueOfFinancialInstrumentsFairValueOfNotesDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDebtAdditionalInformationDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureDebtAdditionalInformationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDebtScheduleOfDebtObligationsDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureDebtScheduleOfDebtObligationsDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/DisclosureDebtScheduleOfDebtObligationsParentheticalDetails" xlink:href="ck0001925309-20221231.xsd#DisclosureDebtScheduleOfDebtObligationsParentheticalDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDebtScheduleOfComponentsOfInterestExpenseDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureDebtScheduleOfComponentsOfInterestExpenseDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesScheduleOfCommitmentsToFundInvestmentsInCurrentPortfolioCompaniesDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureCommitmentsAndContingenciesScheduleOfCommitmentsToFundInvestmentsInCurrentPortfolioCompaniesDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesAdditionalInformationDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureCommitmentsAndContingenciesAdditionalInformationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureNetAssetsAdditionalInformationDetails" xlink:href="ck0001925309-20221231.xsd#Role_DisclosureNetAssetsAdditionalInformationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetails" xlink:href="ck0001925309-20221231.xsd#DisclosureIncomeTaxesAdditionalInformationDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://sixthstreet.com/20221231/taxonomy/role/DisclosureFinancialHighlightsSummaryOfFinancialHighlightsForOneShareCommonStockOutstandingDetails" xlink:href="ck0001925309-20221231.xsd#DisclosureFinancialHighlightsSummaryOfFinancialHighlightsForOneShareCommonStockOutstandingDetails" xlink:type="simple"/>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-roles-2022.xsd#eedm" xlink:type="simple"/>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedBalanceSheet1">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NonControlledNonAffiliatedInvestmentsMember" xlink:label="ck0001925309_NonControlledNonAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAbstract" xlink:label="us-gaap_LiabilitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt" xlink:label="us-gaap_LongTermDebt"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentOwnedAtFairValue" xlink:label="us-gaap_InvestmentOwnedAtFairValue"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NonControlledAffiliatedInvestmentsMember" xlink:label="ck0001925309_NonControlledAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ManagementFeePayable" xlink:label="us-gaap_ManagementFeePayable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalCommonStock" xlink:label="us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ControlledAffiliatedInvestmentsMember" xlink:label="ck0001925309_ControlledAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IncentiveFeesOnNetInvestmentIncomePayableToAffiliate" xlink:label="ck0001925309_IncentiveFeesOnNetInvestmentIncomePayableToAffiliate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestReceivable" xlink:label="us-gaap_InterestReceivable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DueToAffiliateCurrentAndNoncurrent" xlink:label="us-gaap_DueToAffiliateCurrentAndNoncurrent"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsNet" xlink:label="us-gaap_AssetsNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PrepaidExpenseAndOtherAssets" xlink:label="us-gaap_PrepaidExpenseAndOtherAssets"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherLiabilities" xlink:label="us-gaap_OtherLiabilities"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetAssetValuePerShare" xlink:label="us-gaap_NetAssetValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_NonControlledNonAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AssetsAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAbstract" xlink:to="us-gaap_LongTermDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_CommonStockValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_InvestmentOwnedAtFairValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_NonControlledAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LiabilitiesAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAbstract" xlink:to="us-gaap_ManagementFeePayable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_AdditionalPaidInCapitalCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_ControlledAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommitmentsAndContingencies" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAbstract" xlink:to="ck0001925309_IncentiveFeesOnNetInvestmentIncomePayableToAffiliate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_InterestReceivable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquityAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAbstract" xlink:to="us-gaap_DueToAffiliateCurrentAndNoncurrent" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_AssetsNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_PrepaidExpenseAndOtherAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAbstract" xlink:to="us-gaap_OtherLiabilities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_Assets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetAssetValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAbstract" xlink:to="us-gaap_Liabilities" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedBalanceSheetParenthetical">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NonControlledNonAffiliatedInvestmentsMember" xlink:label="ck0001925309_NonControlledNonAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentOwnedAtCost" xlink:label="us-gaap_InvestmentOwnedAtCost"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NonControlledAffiliatedInvestmentsMember" xlink:label="ck0001925309_NonControlledAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedCash" xlink:label="us-gaap_RestrictedCash"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ControlledAffiliatedInvestmentsMember" xlink:label="ck0001925309_ControlledAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsNet" xlink:label="us-gaap_DeferredFinanceCostsNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="us-gaap_PreferredStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockShares" xlink:label="us-gaap_TreasuryStockShares"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_NonControlledNonAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentOwnedAtCost" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_NonControlledAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RestrictedCash" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_ControlledAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DeferredFinanceCostsNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesAuthorized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockShares" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedStatementOfOperations">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_UnRealizedInvestmentGainsLossesAbstract" xlink:label="ck0001925309_UnRealizedInvestmentGainsLossesAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnrealizedGainLossOnInvestments" xlink:label="us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NonControlledNonAffiliatedInvestmentsMember" xlink:label="ck0001925309_NonControlledNonAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RealizedInvestmentGainsLossesAbstract" xlink:label="us-gaap_RealizedInvestmentGainsLossesAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ForeignCurrencyTransactionGainLossRealized" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossRealized"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="us-gaap_OperatingExpensesAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpense" xlink:label="us-gaap_InterestExpense"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrencyAbstract" xlink:label="us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrencyAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="us-gaap_InvestmentIncomeInterest"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ForeignCurrencyTransactionGainLossUnrealized" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossUnrealized"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NonControlledAffiliatedInvestmentsMember" xlink:label="ck0001925309_NonControlledAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NetChangeInRealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation" xlink:label="ck0001925309_NetChangeInRealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ManagementFeeExpense" xlink:label="us-gaap_ManagementFeeExpense"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNonoperatingIncome" xlink:label="us-gaap_OtherNonoperatingIncome"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NetChangeInUnrealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation" xlink:label="ck0001925309_NetChangeInUnrealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ControlledAffiliatedInvestmentsMember" xlink:label="ck0001925309_ControlledAffiliatedInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IncentiveFeesOnNetInvestmentIncome" xlink:label="ck0001925309_IncentiveFeesOnNetInvestmentIncome"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="us-gaap_NonoperatingIncomeExpense"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OrganizationalFees" xlink:label="ck0001925309_OrganizationalFees"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OfferingFees" xlink:label="ck0001925309_OfferingFees"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentIncomeNet" xlink:label="us-gaap_InvestmentIncomeNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfessionalFees" xlink:label="us-gaap_ProfessionalFees"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TrusteeFees" xlink:label="us-gaap_TrusteeFees"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrency" xlink:label="us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrency"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherGeneralAndAdministrativeExpense" xlink:label="us-gaap_OtherGeneralAndAdministrativeExpense"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyNetAssetsFromOperationsIncreaseDecrease" xlink:label="us-gaap_InvestmentCompanyNetAssetsFromOperationsIncreaseDecrease"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingExpenses" xlink:label="us-gaap_OperatingExpenses"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareBasic" xlink:label="us-gaap_EarningsPerShareBasic"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ManagementFeeWaived" xlink:label="ck0001925309_ManagementFeeWaived"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NetExpense" xlink:label="ck0001925309_NetExpense"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_UnRealizedInvestmentGainsLossesAbstract" xlink:to="us-gaap_UnrealizedGainLossOnInvestments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_NonControlledNonAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RealizedInvestmentGainsLossesAbstract" xlink:to="us-gaap_ForeignCurrencyTransactionGainLossRealized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_InterestExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrencyAbstract" xlink:to="ck0001925309_UnRealizedInvestmentGainsLossesAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NonoperatingIncomeExpenseAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_InvestmentIncomeInterest" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_UnRealizedInvestmentGainsLossesAbstract" xlink:to="us-gaap_ForeignCurrencyTransactionGainLossUnrealized" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_NonControlledAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RealizedInvestmentGainsLossesAbstract" xlink:to="ck0001925309_NetChangeInRealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_ManagementFeeExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrencyAbstract" xlink:to="us-gaap_RealizedInvestmentGainsLossesAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingExpensesAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_OtherNonoperatingIncome" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_UnRealizedInvestmentGainsLossesAbstract" xlink:to="ck0001925309_NetChangeInUnrealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_ControlledAffiliatedInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="ck0001925309_IncentiveFeesOnNetInvestmentIncome" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_NonoperatingIncomeExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="ck0001925309_OrganizationalFees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="ck0001925309_OfferingFees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentIncomeNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_ProfessionalFees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrencyAbstract" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_TrusteeFees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrency" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OtherGeneralAndAdministrativeExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentCompanyNetAssetsFromOperationsIncreaseDecrease" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OperatingExpenses" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EarningsPerShareBasic" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="ck0001925309_ManagementFeeWaived" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="ck0001925309_NetExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EarningsPerShareDiluted" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedScheduleOfInvestments1">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_HornetsecurityHoldingGmbhMember" xlink:label="ck0001925309_HornetsecurityHoldingGmbhMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis" xlink:label="us-gaap_VariableRateAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain" xlink:label="us-gaap_VariableRateDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain" xlink:label="us-gaap_VariableRateDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesMember" xlink:label="us-gaap_DebtSecuritiesMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ClassAOneUnitsMember" xlink:label="ck0001925309_ClassAOneUnitsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquitySecuritiesByIndustryAxis" xlink:label="us-gaap_EquitySecuritiesByIndustryAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquitySecuritiesIndustryMember" xlink:label="us-gaap_EquitySecuritiesIndustryMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquitySecuritiesIndustryMember" xlink:label="us-gaap_EquitySecuritiesIndustryMember_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InvestmentOwnedInitialAcquisitionDate" xlink:label="ck0001925309_InvestmentOwnedInitialAcquisitionDate"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EuroInterbankOfferRateMember" xlink:label="ck0001925309_EuroInterbankOfferRateMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BusinessServicesMember" xlink:label="ck0001925309_BusinessServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyNineMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyNineMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OutsystemsLuxcoSarlMember" xlink:label="ck0001925309_OutsystemsLuxcoSarlMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EquityAndOtherInvestmentsMember" xlink:label="ck0001925309_EquityAndOtherInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ClassAUnitsMember" xlink:label="ck0001925309_ClassAUnitsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InvestmentReferenceRate" xlink:label="ck0001925309_InvestmentReferenceRate"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SterlingOvernightInterbankAverageRateMember" xlink:label="ck0001925309_SterlingOvernightInterbankAverageRateMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ChemicalsMember" xlink:label="ck0001925309_ChemicalsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ErlingLuxBidcoSarlMember" xlink:label="ck0001925309_ErlingLuxBidcoSarlMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ClassBUnitsMember" xlink:label="ck0001925309_ClassBUnitsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentInterestRate" xlink:label="us-gaap_InvestmentInterestRate"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecuredOvernightFinancingRateMember" xlink:label="ck0001925309_SecuredOvernightFinancingRateMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FinancialServicesMember" xlink:label="ck0001925309_FinancialServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightOneMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BtrsHoldingsIncMember" xlink:label="ck0001925309_BtrsHoldingsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentOwnedAtCost" xlink:label="us-gaap_InvestmentOwnedAtCost"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_HumanResourceSupportServicesMember" xlink:label="ck0001925309_HumanResourceSupportServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightTwoMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PingIdentityHoldingCorporationMember" xlink:label="ck0001925309_PingIdentityHoldingCorporationMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentOwnedAtFairValue" xlink:label="us-gaap_InvestmentOwnedAtFairValue"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InternetServicesMember" xlink:label="ck0001925309_InternetServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BswiftLlcMember" xlink:label="ck0001925309_BswiftLlcMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentOwnedPercentOfNetAssets" xlink:label="us-gaap_InvestmentOwnedPercentOfNetAssets"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ManufacturingMember" xlink:label="ck0001925309_ManufacturingMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyNineMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyNineMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SMATechnologiesHoldingsLLCMember" xlink:label="ck0001925309_SMATechnologiesHoldingsLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RetailAndConsumerProductsMember" xlink:label="ck0001925309_RetailAndConsumerProductsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AvalaraIncMember" xlink:label="ck0001925309_AvalaraIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BedBathAndBeyondIncMember" xlink:label="ck0001925309_BedBathAndBeyondIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightOneMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_CommercehubIncMember" xlink:label="ck0001925309_CommercehubIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanDueAugustTwoThousandTwentySevenMember" xlink:label="ck0001925309_AblFiloTermLoanDueAugustTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanDueAugustTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienRevolvingLoanDueAugustTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyFiveMember" xlink:label="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightMember" xlink:label="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueDecemberTwoThousandTwentyFourMember" xlink:label="ck0001925309_ConvertibleNoteDueDecemberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineMember" xlink:label="ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecondLienLoanDueJuneTwoThousandTwentyFiveMember" xlink:label="ck0001925309_SecondLienLoanDueJuneTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoThreeMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanOneDueDecemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanOneDueDecemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanDueAprilTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienRevolvingLoanDueAprilTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourOneMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanJulyTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienRevolvingLoanJulyTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeOneMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveTwoMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueSeptemberTwoThousandTwentyThreeMember" xlink:label="ck0001925309_ConvertibleNoteDueSeptemberTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanMayTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienRevolvingLoanMayTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourTwoMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanJuneTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienRevolvingLoanJuneTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyOneMember" xlink:label="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNotesDueJuneTwoThousandTwentySevenMember" xlink:label="ck0001925309_ConvertibleNotesDueJuneTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveTwoMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourOneMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixTwoMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourTwoMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveTwoMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanOneDueOctoberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanOneDueOctoberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanOneDueJulyTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanOneDueJulyTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienNoteDueJuneTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienNoteDueJuneTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienNoteOneDueJuneTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienNoteOneDueJuneTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFILOTermLoanMember" xlink:label="ck0001925309_ABLFILOTermLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanDueSeptemberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_AblFiloTermLoanDueSeptemberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblDipTermLoanDueAprilTwoThousandTwentyOneMember" xlink:label="ck0001925309_AblDipTermLoanDueAprilTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienSecuredNoteDueJulyTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienSecuredNoteDueJulyTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanDueMayTwoThousandTwentyFourMember" xlink:label="ck0001925309_AblFiloTermLoanDueMayTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanDueDecemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_AblFiloTermLoanDueDecemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienTermLoanDueSeptemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienTermLoanDueSeptemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienTermLoanDueDecemberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienTermLoanDueDecemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveThreeMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourThreeMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMarchTwentyTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueMarchTwentyTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMarchTwentyTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueMarchTwentyTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMarchTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueMarchTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanOneDueMarchTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanOneDueMarchTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourThreeMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoOneMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentyFiveMember" xlink:label="ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixTwoMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixThreeMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SubordinatedNoteDueSeptemberTwoThousandTwentySixMember" xlink:label="ck0001925309_SubordinatedNoteDueSeptemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFirstLienLoanDueAugustTwoThousandTwentyFiveMember" xlink:label="ck0001925309_AblFirstLienLoanDueAugustTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFILOTermLoanDueAprilTwoThousandTwentyFourMember" xlink:label="ck0001925309_ABLFILOTermLoanDueAprilTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanOneDueAprilTwoThousandTwentyFourMember" xlink:label="ck0001925309_AblFiloTermLoanOneDueAprilTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentySixMember" xlink:label="ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanParDueSeptemberTwoThousandTwentyOneMember" xlink:label="ck0001925309_FirstLienLoanParDueSeptemberTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanParDueSeptemberTwoThousandTwentyOneMember" xlink:label="ck0001925309_FirstLienRevolvingLoanParDueSeptemberTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixThreeMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenTwoMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TrustCertificatesOneMember" xlink:label="ck0001925309_TrustCertificatesOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TrustCertificatesTwoMember" xlink:label="ck0001925309_TrustCertificatesTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneOneMember" xlink:label="ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneTwoMember" xlink:label="ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_StructuredProductDueJanuaryTwoThousandThirtyMember" xlink:label="ck0001925309_StructuredProductDueJanuaryTwoThousandThirtyMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanMember" xlink:label="ck0001925309_FirstLienLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteMember" xlink:label="ck0001925309_ConvertibleNoteMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecondLienLoanMember" xlink:label="ck0001925309_SecondLienLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanMember" xlink:label="ck0001925309_FirstLienRevolvingLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SubordinatedNoteMember" xlink:label="ck0001925309_SubordinatedNoteMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFirstLienLoanMember" xlink:label="ck0001925309_ABLFirstLienLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_PartnershipInterestMember" xlink:label="srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_HornetsecurityHoldingGmbhMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_VariableRateAxis" xlink:to="us-gaap_VariableRateDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_VariableRateAxis" xlink:to="us-gaap_VariableRateDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="us-gaap_DebtSecuritiesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="ck0001925309_ClassAOneUnitsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_EquitySecuritiesByIndustryAxis" xlink:to="us-gaap_EquitySecuritiesIndustryMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_EquitySecuritiesByIndustryAxis" xlink:to="us-gaap_EquitySecuritiesIndustryMember_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_InvestmentOwnedInitialAcquisitionDate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_EuroInterbankOfferRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_BusinessServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyNineMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_EquitySecuritiesByIndustryAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_OutsystemsLuxcoSarlMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_EquityAndOtherInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="ck0001925309_ClassAUnitsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_InvestmentReferenceRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_SterlingOvernightInterbankAverageRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_ChemicalsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_ErlingLuxBidcoSarlMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="ck0001925309_ClassBUnitsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentInterestRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_SecuredOvernightFinancingRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_FinancialServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_DebtInstrumentAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_BtrsHoldingsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentOwnedAtCost" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_HumanResourceSupportServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_PingIdentityHoldingCorporationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentOwnedAtFairValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_InternetServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_VariableRateAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_BswiftLlcMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentOwnedPercentOfNetAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_ManufacturingMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyNineMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_SMATechnologiesHoldingsLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_RetailAndConsumerProductsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_AvalaraIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_BedBathAndBeyondIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_CommercehubIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanDueAugustTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanDueAugustTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="26" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueDecemberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="27" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="28" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SecondLienLoanDueJuneTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="29" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="30" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="31" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="32" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="33" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="34" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="35" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="36" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="37" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="38" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="39" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanOneDueDecemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="40" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanDueAprilTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="41" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="42" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="43" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="44" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="45" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="46" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="47" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="48" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="49" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="50" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="51" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="52" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanJulyTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="53" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="54" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="55" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="56" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="57" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="58" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="59" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueSeptemberTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="60" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="61" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanMayTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="62" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="63" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="64" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="65" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanJuneTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="66" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="67" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="68" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="69" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="70" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="71" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="72" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNotesDueJuneTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="73" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="74" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="75" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="76" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="77" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="78" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="79" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="80" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="81" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="82" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanOneDueOctoberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="83" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="84" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanOneDueJulyTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="85" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="86" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="87" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="88" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienNoteDueJuneTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="89" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienNoteOneDueJuneTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="90" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFILOTermLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="91" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanDueSeptemberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="92" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblDipTermLoanDueAprilTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="93" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="94" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienSecuredNoteDueJulyTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="95" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanDueMayTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="96" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanDueDecemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="97" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienTermLoanDueSeptemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="98" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienTermLoanDueDecemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="99" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="100" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="101" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="102" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="103" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMarchTwentyTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="104" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMarchTwentyTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="105" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="106" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMarchTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="107" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanOneDueMarchTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="108" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="109" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="110" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="111" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="112" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="113" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="114" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="115" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="116" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SubordinatedNoteDueSeptemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="117" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFirstLienLoanDueAugustTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="118" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFILOTermLoanDueAprilTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="119" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanOneDueAprilTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="120" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="121" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanParDueSeptemberTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="122" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="123" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanParDueSeptemberTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="124" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="125" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="126" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="127" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="128" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="129" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TrustCertificatesOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="130" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TrustCertificatesTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="131" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="132" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="133" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_StructuredProductDueJanuaryTwoThousandThirtyMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="134" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="135" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="136" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SecondLienLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="137" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="138" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SubordinatedNoteMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="139" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFirstLienLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="140" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="srt_PartnershipInterestMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedScheduleOfInvestmentsParenthetical">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="us-gaap_IncomeTaxAuthorityDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DomesticCountryMember" xlink:label="us-gaap_DomesticCountryMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_HornetsecurityHoldingGmbhMember" xlink:label="ck0001925309_HornetsecurityHoldingGmbhMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesMember" xlink:label="us-gaap_DebtSecuritiesMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ClassAOneUnitsMember" xlink:label="ck0001925309_ClassAOneUnitsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquitySecuritiesByIndustryAxis" xlink:label="us-gaap_EquitySecuritiesByIndustryAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquitySecuritiesIndustryMember" xlink:label="us-gaap_EquitySecuritiesIndustryMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentOwnedUnderlyingFaceAmountAtMarketValue" xlink:label="us-gaap_InvestmentOwnedUnderlyingFaceAmountAtMarketValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022q3/us-gaap-sup-2022q3.xsd#us-gaap_InvestmentIssuerAffiliationDomain" xlink:label="us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022q3/us-gaap-sup-2022q3.xsd#us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember" xlink:label="us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BusinessServicesMember" xlink:label="ck0001925309_BusinessServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyNineMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyNineMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022q3/us-gaap-sup-2022q3.xsd#us-gaap_InvestmentIssuerAffiliationAxis" xlink:label="us-gaap_InvestmentIssuerAffiliationAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022q3/us-gaap-sup-2022q3.xsd#us-gaap_InvestmentIssuerAffiliationDomain" xlink:label="us-gaap_InvestmentIssuerAffiliationDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="us-gaap_IncomeTaxAuthorityAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="us-gaap_IncomeTaxAuthorityDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OutsystemsLuxcoSarlMember" xlink:label="ck0001925309_OutsystemsLuxcoSarlMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EquityAndOtherInvestmentsMember" xlink:label="ck0001925309_EquityAndOtherInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ClassAUnitsMember" xlink:label="ck0001925309_ClassAUnitsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InvestmentDueDate" xlink:label="ck0001925309_InvestmentDueDate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022q3/us-gaap-sup-2022q3.xsd#us-gaap_InvestmentAffiliatedIssuerControlledMember" xlink:label="us-gaap_InvestmentAffiliatedIssuerControlledMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ChemicalsMember" xlink:label="ck0001925309_ChemicalsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ErlingLuxBidcoSarlMember" xlink:label="ck0001925309_ErlingLuxBidcoSarlMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ClassBUnitsMember" xlink:label="ck0001925309_ClassBUnitsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentOwnedBalanceShares" xlink:label="us-gaap_InvestmentOwnedBalanceShares"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FinancialServicesMember" xlink:label="ck0001925309_FinancialServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightOneMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BtrsHoldingsIncMember" xlink:label="ck0001925309_BtrsHoldingsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfNonQualifyingAssets" xlink:label="ck0001925309_PercentageOfNonQualifyingAssets"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_HumanResourceSupportServicesMember" xlink:label="ck0001925309_HumanResourceSupportServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightTwoMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PingIdentityHoldingCorporationMember" xlink:label="ck0001925309_PingIdentityHoldingCorporationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfMinimumQualifyingAssetsToPurchaseNonQualifyingAssets" xlink:label="ck0001925309_PercentageOfMinimumQualifyingAssetsToPurchaseNonQualifyingAssets"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InternetServicesMember" xlink:label="ck0001925309_InternetServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BswiftLlcMember" xlink:label="ck0001925309_BswiftLlcMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_MinimumPercentageOfVotingSecuritiesInInvestmentPortfolio" xlink:label="ck0001925309_MinimumPercentageOfVotingSecuritiesInInvestmentPortfolio"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ManufacturingMember" xlink:label="ck0001925309_ManufacturingMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyNineMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyNineMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SMATechnologiesHoldingsLLCMember" xlink:label="ck0001925309_SMATechnologiesHoldingsLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TaxCostOfInvestments" xlink:label="ck0001925309_TaxCostOfInvestments"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RetailAndConsumerProductsMember" xlink:label="ck0001925309_RetailAndConsumerProductsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AvalaraIncMember" xlink:label="ck0001925309_AvalaraIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EstimatedGrossUnrealizedGainsOnTaxCostInvestment" xlink:label="ck0001925309_EstimatedGrossUnrealizedGainsOnTaxCostInvestment"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BedBathAndBeyondIncMember" xlink:label="ck0001925309_BedBathAndBeyondIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EstimatedGrossUnrealizedLossOnTaxCostInvestment" xlink:label="ck0001925309_EstimatedGrossUnrealizedLossOnTaxCostInvestment"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightOneMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_CommercehubIncMember" xlink:label="ck0001925309_CommercehubIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FairValueOfSecuritiesAsPercentageOfNetAssetsAmount" xlink:label="ck0001925309_FairValueOfSecuritiesAsPercentageOfNetAssetsAmount"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanDueAugustTwoThousandTwentySevenMember" xlink:label="ck0001925309_AblFiloTermLoanDueAugustTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FairValueOfSecuritiesAsPercentageOfNetAssetsInPercentage" xlink:label="ck0001925309_FairValueOfSecuritiesAsPercentageOfNetAssetsInPercentage"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanDueAugustTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienRevolvingLoanDueAugustTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyFiveMember" xlink:label="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightMember" xlink:label="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueDecemberTwoThousandTwentyFourMember" xlink:label="ck0001925309_ConvertibleNoteDueDecemberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineMember" xlink:label="ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecondLienLoanDueJuneTwoThousandTwentyFiveMember" xlink:label="ck0001925309_SecondLienLoanDueJuneTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoThreeMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourOneMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanOneDueDecemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanOneDueDecemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanDueAprilTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienRevolvingLoanDueAprilTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanJulyTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienRevolvingLoanJulyTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanMayTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienRevolvingLoanMayTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanMember" xlink:label="ck0001925309_FirstLienLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteMember" xlink:label="ck0001925309_ConvertibleNoteMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanMember" xlink:label="ck0001925309_FirstLienRevolvingLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienNoteDueJuneTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienNoteDueJuneTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienNoteOneDueJuneTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienNoteOneDueJuneTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFILOTermLoanMember" xlink:label="ck0001925309_ABLFILOTermLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanDueSeptemberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_AblFiloTermLoanDueSeptemberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblDipTermLoanDueAprilTwoThousandTwentyOneMember" xlink:label="ck0001925309_AblDipTermLoanDueAprilTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienSecuredNoteDueJulyTwoThousandTwentyThreeMember" xlink:label="ck0001925309_FirstLienSecuredNoteDueJulyTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanDueMayTwoThousandTwentyFourMember" xlink:label="ck0001925309_AblFiloTermLoanDueMayTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanDueDecemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_AblFiloTermLoanDueDecemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienTermLoanDueSeptemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienTermLoanDueSeptemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienTermLoanDueDecemberTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienTermLoanDueDecemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyOneMember" xlink:label="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SubordinatedNoteMember" xlink:label="ck0001925309_SubordinatedNoteMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TrustCertificatesOneMember" xlink:label="ck0001925309_TrustCertificatesOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TrustCertificatesTwoMember" xlink:label="ck0001925309_TrustCertificatesTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneMember" xlink:label="ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_StructuredProductDueJanuaryTwoThousandThirtyMember" xlink:label="ck0001925309_StructuredProductDueJanuaryTwoThousandThirtyMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanParDueSeptemberTwoThousandTwentyOneMember" xlink:label="ck0001925309_FirstLienLoanParDueSeptemberTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanParDueSeptemberTwoThousandTwentyOneMember" xlink:label="ck0001925309_FirstLienRevolvingLoanParDueSeptemberTwoThousandTwentyOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveThreeMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveTwoMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenThreeMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenOneMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixFourMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixFourMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixTwoMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixTwoMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightOneMember" xlink:label="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineOneMember" xlink:label="ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixTwoMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeTwoMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoOneMember" xlink:label="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourOneMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourThreeMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMarchTwentyTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueMarchTwentyTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMarchTwentyTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueMarchTwentyTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFirstLienLoanDueAugustTwoThousandTwentyFiveMember" xlink:label="ck0001925309_AblFirstLienLoanDueAugustTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourFourMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeOneMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenOneMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightOneMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixThreeMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveThreeMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveFourMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveTwoMember" xlink:label="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveThreeMember" xlink:label="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenOneMember" xlink:label="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNoteDueSeptemberTwoThousandTwentyThreeMember" xlink:label="ck0001925309_ConvertibleNoteDueSeptemberTwoThousandTwentyThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanDueMayTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienRevolvingLoanDueMayTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourThreeMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanJuneTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienRevolvingLoanJuneTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleNotesDueJuneTwoThousandTwentySevenMember" xlink:label="ck0001925309_ConvertibleNotesDueJuneTwoThousandTwentySevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveTwoMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourOneMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixTwoMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourTwoMember" xlink:label="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveTwoMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanOneDueOctoberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanOneDueOctoberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanOneDueJulyTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanOneDueJulyTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoansDueDecemberTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoansDueDecemberTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoMember" xlink:label="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoansDueDecemberTwoThousandTwentyFiveMember" xlink:label="ck0001925309_FirstLienLoansDueDecemberTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMarchTwoThousandTwentySixMember" xlink:label="ck0001925309_FirstLienLoanDueMarchTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoansDueAugustTwoThousandTwentyFiveOneMember" xlink:label="ck0001925309_FirstLienLoansDueAugustTwoThousandTwentyFiveOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixOneMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixOneMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixSevenMember" xlink:label="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixSevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueMarchTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanDueMarchTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanOneDueMarchTwoThousandTwentyFourMember" xlink:label="ck0001925309_FirstLienLoanOneDueMarchTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentyFiveMember" xlink:label="ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentyFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SubordinatedNoteDueSeptemberTwoThousandTwentySixMember" xlink:label="ck0001925309_SubordinatedNoteDueSeptemberTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFirstLienLoanMember" xlink:label="ck0001925309_ABLFirstLienLoanMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFILOTermLoanDueAprilTwoThousandTwentyFourMember" xlink:label="ck0001925309_ABLFILOTermLoanDueAprilTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AblFiloTermLoanOneDueAprilTwoThousandTwentyFourMember" xlink:label="ck0001925309_AblFiloTermLoanOneDueAprilTwoThousandTwentyFourMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentySixMember" xlink:label="ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentySixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySevenMember" xlink:label="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySevenMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeTaxAuthorityDomain" xlink:to="us-gaap_DomesticCountryMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_HornetsecurityHoldingGmbhMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="us-gaap_DebtSecuritiesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="ck0001925309_ClassAOneUnitsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_EquitySecuritiesByIndustryAxis" xlink:to="us-gaap_EquitySecuritiesIndustryMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentOwnedUnderlyingFaceAmountAtMarketValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentIssuerAffiliationDomain" xlink:to="us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_BusinessServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyNineMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentIssuerAffiliationAxis" xlink:to="us-gaap_InvestmentIssuerAffiliationDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_InvestmentIssuerAffiliationAxis" xlink:to="us-gaap_InvestmentIssuerAffiliationDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeTaxAuthorityAxis" xlink:to="us-gaap_IncomeTaxAuthorityDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_IncomeTaxAuthorityAxis" xlink:to="us-gaap_IncomeTaxAuthorityDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_EquitySecuritiesByIndustryAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_OutsystemsLuxcoSarlMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_EquityAndOtherInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="ck0001925309_ClassAUnitsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_InvestmentDueDate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentIssuerAffiliationDomain" xlink:to="us-gaap_InvestmentAffiliatedIssuerControlledMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_ChemicalsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_ErlingLuxBidcoSarlMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="ck0001925309_ClassBUnitsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentOwnedBalanceShares" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_FinancialServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InvestmentIssuerAffiliationAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_BtrsHoldingsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_PercentageOfNonQualifyingAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_HumanResourceSupportServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyEightTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_DebtInstrumentAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_PingIdentityHoldingCorporationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_PercentageOfMinimumQualifyingAssetsToPurchaseNonQualifyingAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_InternetServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyEightOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementClassOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_BswiftLlcMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_MinimumPercentageOfVotingSecuritiesInInvestmentPortfolio" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_ManufacturingMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyNineMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_IncomeTaxAuthorityAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_SMATechnologiesHoldingsLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_TaxCostOfInvestments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_RetailAndConsumerProductsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_AvalaraIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_EstimatedGrossUnrealizedGainsOnTaxCostInvestment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_BedBathAndBeyondIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_EstimatedGrossUnrealizedLossOnTaxCostInvestment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyEightOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="ck0001925309_CommercehubIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_FairValueOfSecuritiesAsPercentageOfNetAssetsAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanDueAugustTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_FairValueOfSecuritiesAsPercentageOfNetAssetsInPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanDueAugustTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="26" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="27" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="28" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueDecemberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="29" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="30" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="31" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="32" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SecondLienLoanDueJuneTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="33" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="34" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="35" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="36" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="37" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="38" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="39" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="40" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="41" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="42" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="43" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="44" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="45" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="46" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanOneDueDecemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="47" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="48" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="49" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="50" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanDueAprilTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="51" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="52" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="53" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="54" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="55" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="56" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanJulyTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="57" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="58" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="59" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="60" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanMayTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="61" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="62" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="63" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="64" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienNoteDueJuneTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="65" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienNoteOneDueJuneTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="66" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFILOTermLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="67" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanDueSeptemberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="68" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblDipTermLoanDueAprilTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="69" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="70" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienSecuredNoteDueJulyTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="71" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanDueMayTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="72" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanDueDecemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="73" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienTermLoanDueSeptemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="74" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienTermLoanDueDecemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="75" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="76" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SubordinatedNoteMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="77" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TrustCertificatesOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="78" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TrustCertificatesTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="79" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_StructuredProductDueAprilTwoThousandThirtyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="80" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_StructuredProductDueJanuaryTwoThousandThirtyMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="81" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanParDueSeptemberTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="82" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanParDueSeptemberTwoThousandTwentyOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="83" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="84" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyFiveTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="85" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySevenThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="86" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentySevenOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="87" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="88" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="89" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="90" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentySixTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="91" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="92" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySixTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="93" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFourOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="94" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueMayTwoThousandTwentyEightOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="95" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SecondLienLoanDueOctoberTwoThousandTwentyNineOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="96" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="97" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentyThreeTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="98" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAugustTwoThousandTwentyTwoOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="99" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFourOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="100" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="101" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMarchTwentyTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="102" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMarchTwentyTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="103" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFirstLienLoanDueAugustTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="104" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFourFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="105" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyThreeOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="106" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySevenOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="107" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyEightOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="108" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentySixThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="109" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="110" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentyFiveFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="111" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="112" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanAprilTwoThousandTwentyFiveThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="113" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanDueOctoberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="114" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="115" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyThreeOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="116" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueAprilTwoThousandTwentySevenOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="117" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNoteDueSeptemberTwoThousandTwentyThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="118" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="119" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanDueMayTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="120" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJuneTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="121" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="122" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanJuneTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="123" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="124" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="125" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienRevolvingLoanOctoberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="126" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="127" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ConvertibleNotesDueJuneTwoThousandTwentySevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="128" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="129" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="130" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyFiveTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="131" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="132" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentySixTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="133" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMayTwoThousandTwentyFourTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="134" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyFiveTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="135" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJanuaryTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="136" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueOctoberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="137" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanOneDueOctoberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="138" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueJulyTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="139" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanOneDueJulyTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="140" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueFebruaryTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="141" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoansDueDecemberTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="142" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueDecemberTwoThousandTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="143" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoansDueDecemberTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="144" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMarchTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="145" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoansDueAugustTwoThousandTwentyFiveOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="146" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="147" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueSeptemberTwoThousandTwentySixSevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="148" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueMarchTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="149" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanOneDueMarchTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="150" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentyFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="151" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_SubordinatedNoteDueSeptemberTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="152" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFirstLienLoanMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="153" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFILOTermLoanDueAprilTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="154" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_AblFiloTermLoanOneDueAprilTwoThousandTwentyFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="155" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_ABLFILOTermLoanDueMayTwoThousandTwentySixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="156" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_FirstLienLoanDueNovemberTwoThousandTwentySevenMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/StatementConsolidatedStatementsOfChangesInNetAssets">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding" xlink:label="us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockMember" xlink:label="us-gaap_TreasuryStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentIncomeNet" xlink:label="us-gaap_InvestmentIncomeNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NetChangeInUnrealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation" xlink:label="ck0001925309_NetChangeInUnrealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NetRealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation" xlink:label="ck0001925309_NetRealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockSharesAcquired" xlink:label="us-gaap_TreasuryStockSharesAcquired"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RepurchaseOfConvertibleNotes" xlink:label="ck0001925309_RepurchaseOfConvertibleNotes"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan" xlink:label="us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan" xlink:label="us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Dividends" xlink:label="us-gaap_Dividends"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TaxReclassificationOfStockholdersEquity" xlink:label="ck0001925309_TaxReclassificationOfStockholdersEquity"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharesOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_TreasuryStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentIncomeNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AdditionalPaidInCapitalMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_NetChangeInUnrealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_NetRealizedGainsLossesOnInvestmentsAndForeignCurrencyTranslation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockValueAcquiredCostMethod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockSharesAcquired" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_RepurchaseOfConvertibleNotes" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_Dividends" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="ck0001925309_TaxReclassificationOfStockholdersEquity" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/cef/role/RiskOnly">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/cef/2022/cef-2022.xsd#cef_AllRisksMember" xlink:label="cef_AllRisksMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RisksRelatedToOurBusinessAndStructureMember" xlink:label="ck0001925309_RisksRelatedToOurBusinessAndStructureMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RisksRelatedToEconomicConditionsMember" xlink:label="ck0001925309_RisksRelatedToEconomicConditionsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RisksRelatedToOurPortfolioCompanyInvestmentsMember" xlink:label="ck0001925309_RisksRelatedToOurPortfolioCompanyInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RisksRelatedToOurSecuritiesMember" xlink:label="ck0001925309_RisksRelatedToOurSecuritiesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_GeneralRiskFactorsMember" xlink:label="ck0001925309_GeneralRiskFactorsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FederalIncomeTaxRisksMember" xlink:label="ck0001925309_FederalIncomeTaxRisksMember"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllRisksMember" xlink:to="ck0001925309_RisksRelatedToOurBusinessAndStructureMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllRisksMember" xlink:to="ck0001925309_RisksRelatedToEconomicConditionsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllRisksMember" xlink:to="ck0001925309_RisksRelatedToOurPortfolioCompanyInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllRisksMember" xlink:to="ck0001925309_RisksRelatedToOurSecuritiesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllRisksMember" xlink:to="ck0001925309_GeneralRiskFactorsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllRisksMember" xlink:to="ck0001925309_FederalIncomeTaxRisksMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/cef/role/SecurityOnly">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/cef/2022/cef-2022.xsd#cef_AllSecuritiesMember" xlink:label="cef_AllSecuritiesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RevolvingCreditsFacilitiesMember" xlink:label="ck0001925309_RevolvingCreditsFacilitiesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleSeniorNotesDueTwentyNineteenMember" xlink:label="ck0001925309_ConvertibleSeniorNotesDueTwentyNineteenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ConvertibleSeniorNotesDueTwentyTwentyTwoMember" xlink:label="ck0001925309_ConvertibleSeniorNotesDueTwentyTwentyTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyNineteenConvertibleNotesMember" xlink:label="ck0001925309_TwentyNineteenConvertibleNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyTwentyTwoConvertibleNotesMember" xlink:label="ck0001925309_TwentyTwentyTwoConvertibleNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyTwentyThreeNotesMember" xlink:label="ck0001925309_TwentyTwentyThreeNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyTwentyFourNotesMember" xlink:label="ck0001925309_TwentyTwentyFourNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyTwentySixNotesMember" xlink:label="ck0001925309_TwentyTwentySixNotesMember"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllSecuritiesMember" xlink:to="ck0001925309_RevolvingCreditsFacilitiesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllSecuritiesMember" xlink:to="ck0001925309_ConvertibleSeniorNotesDueTwentyNineteenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllSecuritiesMember" xlink:to="ck0001925309_ConvertibleSeniorNotesDueTwentyTwentyTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllSecuritiesMember" xlink:to="ck0001925309_TwentyNineteenConvertibleNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllSecuritiesMember" xlink:to="ck0001925309_TwentyTwentyTwoConvertibleNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllSecuritiesMember" xlink:to="ck0001925309_TwentyTwentyThreeNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllSecuritiesMember" xlink:to="ck0001925309_TwentyTwentyFourNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="cef_AllSecuritiesMember" xlink:to="ck0001925309_TwentyTwentySixNotesMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureSignificantAccountingPoliciesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SignificantAccountingPoliciesLineItems" xlink:label="ck0001925309_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SignificantAccountingPoliciesTable" xlink:label="ck0001925309_SignificantAccountingPoliciesTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfOrganizationAndOfferingExpenses" xlink:label="ck0001925309_PercentageOfOrganizationAndOfferingExpenses"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OrganizationAndOfferingExpenses" xlink:label="ck0001925309_OrganizationAndOfferingExpenses"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_MinimumPercentageOfInvestmentCompanyTaxableIncomeDistributeToStockholdersInEachTaxableYearToQualifyAsRIC" xlink:label="ck0001925309_MinimumPercentageOfInvestmentCompanyTaxableIncomeDistributeToStockholdersInEachTaxableYearToQualifyAsRIC"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="us-gaap_UnrecognizedTaxBenefits"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NondeductibleFederalExciseTaxPercentage" xlink:label="ck0001925309_NondeductibleFederalExciseTaxPercentage"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NetExpenseForFederalExciseTaxAndOtherTaxes" xlink:label="ck0001925309_NetExpenseForFederalExciseTaxAndOtherTaxes"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateEarlyAdoption" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateEarlyAdoption"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdoptionDate" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdoptionDate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateImmaterialEffect" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateImmaterialEffect"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountingStandardsUpdateExtensibleList" xlink:label="us-gaap_AccountingStandardsUpdateExtensibleList"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="ck0001925309_SignificantAccountingPoliciesTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ck0001925309_SignificantAccountingPoliciesTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="ck0001925309_PercentageOfOrganizationAndOfferingExpenses" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="ck0001925309_OrganizationAndOfferingExpenses" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="ck0001925309_MinimumPercentageOfInvestmentCompanyTaxableIncomeDistributeToStockholdersInEachTaxableYearToQualifyAsRIC" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="us-gaap_UnrecognizedTaxBenefits" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="ck0001925309_NondeductibleFederalExciseTaxPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="ck0001925309_NetExpenseForFederalExciseTaxAndOtherTaxes" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateEarlyAdoption" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdoptionDate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateImmaterialEffect" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ck0001925309_SignificantAccountingPoliciesLineItems" xlink:to="us-gaap_AccountingStandardsUpdateExtensibleList" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureAgreementsAndRelatedPartyTransactionsAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="srt_ScenarioUnspecifiedDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScenarioForecastMember" xlink:label="srt_ScenarioForecastMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AdviserMember" xlink:label="ck0001925309_AdviserMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementScenarioAxis" xlink:label="srt_StatementScenarioAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="srt_ScenarioUnspecifiedDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="us-gaap_RelatedPartyTransactionAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="us-gaap_RelatedPartyTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="us-gaap_RelatedPartyTransactionDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AdministrationAgreementMember" xlink:label="ck0001925309_AdministrationAgreementMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AgreementTerminationPeriodWithoutPenalty" xlink:label="ck0001925309_AgreementTerminationPeriodWithoutPenalty"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_CapitalGainsAccrueFollowingMarchThirtyFirstTwoThousandFourteenMember" xlink:label="ck0001925309_CapitalGainsAccrueFollowingMarchThirtyFirstTwoThousandFourteenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_LeverageWaiverMember" xlink:label="ck0001925309_LeverageWaiverMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InvestmentAdvisoryAgreementMember" xlink:label="ck0001925309_InvestmentAdvisoryAgreementMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" xlink:label="us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RealizedCapitalGainsAccruedPriorToMarchThirtyFirstTwoThousandFourteenMember" xlink:label="ck0001925309_RealizedCapitalGainsAccruedPriorToMarchThirtyFirstTwoThousandFourteenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfManagementFeeCalculatedOnGrossAssets" xlink:label="ck0001925309_PercentageOfManagementFeeCalculatedOnGrossAssets"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RealizedCapitalGainsAccruedBeginningAprilFirstTwoThousandFourteenMember" xlink:label="ck0001925309_RealizedCapitalGainsAccruedBeginningAprilFirstTwoThousandFourteenMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ManagementFeeExpense" xlink:label="us-gaap_ManagementFeeExpense"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FutureRealizedCapitalGainsPriorToAprilFirstTwoThousandFourteenMember" xlink:label="ck0001925309_FutureRealizedCapitalGainsPriorToAprilFirstTwoThousandFourteenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ManagementFeesGrossOfWaivers" xlink:label="ck0001925309_ManagementFeesGrossOfWaivers"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfManagementFeesInExcessOfAverageAggregateDrawnCapital" xlink:label="ck0001925309_PercentageOfManagementFeesInExcessOfAverageAggregateDrawnCapital"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfExcessPreIncentiveFeeNetInvestmentIncomeForImmediatePrecedingCalendarQuarter" xlink:label="ck0001925309_PercentageOfExcessPreIncentiveFeeNetInvestmentIncomeForImmediatePrecedingCalendarQuarter"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ManagementFeeWaiverHurdle" xlink:label="ck0001925309_ManagementFeeWaiverHurdle"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfManagementFeeInExcessOfAnnualRateOnGrossAssets" xlink:label="ck0001925309_PercentageOfManagementFeeInExcessOfAnnualRateOnGrossAssets"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfManagementFeeInExcessOfQuarterRateOnGrossAssets" xlink:label="ck0001925309_PercentageOfManagementFeeInExcessOfQuarterRateOnGrossAssets"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeHurdleRateQuarterly" xlink:label="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeHurdleRateQuarterly"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableQuarterly" xlink:label="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableQuarterly"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableQuarterlySubsequentToExchangeListing" xlink:label="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableQuarterlySubsequentToExchangeListing"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeQuarterlyAfterCatchUpAchieved" xlink:label="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeQuarterlyAfterCatchUpAchieved"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfAllRemainingPreIncentiveFeeNetInvestmentIncomeQuarterly" xlink:label="ck0001925309_PercentageOfAllRemainingPreIncentiveFeeNetInvestmentIncomeQuarterly"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfAllRemainingPreIncentiveFeeNetInvestmentIncomeQuarterlySubsequentToExchangeListing" xlink:label="ck0001925309_PercentageOfAllRemainingPreIncentiveFeeNetInvestmentIncomeQuarterlySubsequentToExchangeListing"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfCumulativeRealizedCapitalGainsLessAggregateCapitalGainIncentiveFee" xlink:label="ck0001925309_PercentageOfCumulativeRealizedCapitalGainsLessAggregateCapitalGainIncentiveFee"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfCapitalGainIncentiveFeePriorToExchangeListing" xlink:label="ck0001925309_PercentageOfCapitalGainIncentiveFeePriorToExchangeListing"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfCapitalGainIncentiveFeeSubsequentToExchangeListing" xlink:label="ck0001925309_PercentageOfCapitalGainIncentiveFeeSubsequentToExchangeListing"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfExcessCatchUpProvisionForPreIncentiveFeeNetInvestmentIncome" xlink:label="ck0001925309_PercentageOfExcessCatchUpProvisionForPreIncentiveFeeNetInvestmentIncome"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfAllPreIncentiveFeeNetInvestmentIncomeAfterCatchUpAchieved" xlink:label="ck0001925309_PercentageOfAllPreIncentiveFeeNetInvestmentIncomeAfterCatchUpAchieved"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeAnnualizedAfterCatchUpAchieved" xlink:label="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeAnnualizedAfterCatchUpAchieved"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfExcessPreIncentiveFeeNetInvestmentIncomePayableAfterHurdleRateReachedAndCatchUpAchieved" xlink:label="ck0001925309_PercentageOfExcessPreIncentiveFeeNetInvestmentIncomePayableAfterHurdleRateReachedAndCatchUpAchieved"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableAfterHurdleRateReachedAndCatchUpAchieved" xlink:label="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableAfterHurdleRateReachedAndCatchUpAchieved"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfWeightedCumulativeRealizedCapitalGainsLessRealizedCapitalLossesAndUnrealizedCapitalLossesThroughMarch312014HurdleRate" xlink:label="ck0001925309_PercentageOfWeightedCumulativeRealizedCapitalGainsLessRealizedCapitalLossesAndUnrealizedCapitalLossesThroughMarch312014HurdleRate"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfCapitalGainsFromApril12024HurdleRate" xlink:label="ck0001925309_PercentageOfCapitalGainsFromApril12024HurdleRate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Investments" xlink:label="us-gaap_Investments"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfIncentiveFeeRate" xlink:label="ck0001925309_PercentageOfIncentiveFeeRate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncentiveFeeExpense" xlink:label="us-gaap_IncentiveFeeExpense"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IncentiveFeesOnNetInvestmentIncome" xlink:label="ck0001925309_IncentiveFeesOnNetInvestmentIncome"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IncentiveFeesAccruedRelatedToCumulativeUnrealizedCapitalGains" xlink:label="ck0001925309_IncentiveFeesAccruedRelatedToCumulativeUnrealizedCapitalGains"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IncentiveFeesAccruedRelatedToExpenseReversalCapitalGainsFees" xlink:label="ck0001925309_IncentiveFeesAccruedRelatedToExpenseReversalCapitalGainsFees"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="srt_ScenarioForecastMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyDomain" xlink:to="ck0001925309_AdviserMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementScenarioAxis" xlink:to="srt_ScenarioUnspecifiedDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementScenarioAxis" xlink:to="srt_ScenarioUnspecifiedDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_RelatedPartyTransactionAxis" xlink:to="us-gaap_RelatedPartyTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_RelatedPartyTransactionAxis" xlink:to="us-gaap_RelatedPartyTransactionDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionDomain" xlink:to="ck0001925309_AdministrationAgreementMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_GeneralAndAdministrativeExpenseMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_AgreementTerminationPeriodWithoutPenalty" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="us-gaap_RelatedPartyTransactionAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="ck0001925309_CapitalGainsAccrueFollowingMarchThirtyFirstTwoThousandFourteenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyDomain" xlink:to="ck0001925309_LeverageWaiverMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionDomain" xlink:to="ck0001925309_InvestmentAdvisoryAgreementMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="ck0001925309_RealizedCapitalGainsAccruedPriorToMarchThirtyFirstTwoThousandFourteenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfManagementFeeCalculatedOnGrossAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="srt_StatementScenarioAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="ck0001925309_RealizedCapitalGainsAccruedBeginningAprilFirstTwoThousandFourteenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_ManagementFeeExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="us-gaap_IncomeStatementLocationAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="ck0001925309_FutureRealizedCapitalGainsPriorToAprilFirstTwoThousandFourteenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_ManagementFeesGrossOfWaivers" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfManagementFeesInExcessOfAverageAggregateDrawnCapital" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfExcessPreIncentiveFeeNetInvestmentIncomeForImmediatePrecedingCalendarQuarter" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_ManagementFeeWaiverHurdle" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfManagementFeeInExcessOfAnnualRateOnGrossAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfManagementFeeInExcessOfQuarterRateOnGrossAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeHurdleRateQuarterly" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableQuarterly" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableQuarterlySubsequentToExchangeListing" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeQuarterlyAfterCatchUpAchieved" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfAllRemainingPreIncentiveFeeNetInvestmentIncomeQuarterly" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfAllRemainingPreIncentiveFeeNetInvestmentIncomeQuarterlySubsequentToExchangeListing" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfCumulativeRealizedCapitalGainsLessAggregateCapitalGainIncentiveFee" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfCapitalGainIncentiveFeePriorToExchangeListing" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfCapitalGainIncentiveFeeSubsequentToExchangeListing" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfExcessCatchUpProvisionForPreIncentiveFeeNetInvestmentIncome" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfAllPreIncentiveFeeNetInvestmentIncomeAfterCatchUpAchieved" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomeAnnualizedAfterCatchUpAchieved" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfExcessPreIncentiveFeeNetInvestmentIncomePayableAfterHurdleRateReachedAndCatchUpAchieved" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfPreIncentiveFeeNetInvestmentIncomePayableAfterHurdleRateReachedAndCatchUpAchieved" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfWeightedCumulativeRealizedCapitalGainsLessRealizedCapitalLossesAndUnrealizedCapitalLossesThroughMarch312014HurdleRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfCapitalGainsFromApril12024HurdleRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="26" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_Investments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="27" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_PercentageOfIncentiveFeeRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="28" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_IncentiveFeeExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="29" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_IncentiveFeesOnNetInvestmentIncome" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="30" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_IncentiveFeesAccruedRelatedToCumulativeUnrealizedCapitalGains" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="31" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="ck0001925309_IncentiveFeesAccruedRelatedToExpenseReversalCapitalGainsFees" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureInvestmentsAtFairValueAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipAxis" xlink:label="srt_OwnershipAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipDomain" xlink:label="srt_OwnershipDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AffiliatedMember" xlink:label="ck0001925309_AffiliatedMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners" xlink:label="us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipDomain" xlink:label="srt_OwnershipDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage" xlink:label="us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:to="srt_OwnershipAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_OwnershipDomain" xlink:to="ck0001925309_AffiliatedMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_OwnershipAxis" xlink:to="srt_OwnershipDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_OwnershipAxis" xlink:to="srt_OwnershipDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_EquityMethodInvestmentOwnershipPercentage" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureInvestmentsAtFairValueSummaryOfInvestmentsAtFairValueDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienDebtInvestmentsMember" xlink:label="ck0001925309_FirstLienDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecondLienDebtInvestmentsMember" xlink:label="ck0001925309_SecondLienDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_MezzanineDebtInvestmentsMember" xlink:label="ck0001925309_MezzanineDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss" xlink:label="us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EquityAndOtherInvestmentsMember" xlink:label="ck0001925309_EquityAndOtherInvestmentsMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ck0001925309_FirstLienDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:to="us-gaap_FinancialInstrumentAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ck0001925309_SecondLienDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ck0001925309_MezzanineDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ck0001925309_EquityAndOtherInvestmentsMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureInvestmentsAtFairValueSummaryOfIndustryCompositionOfInvestmentsAtFairValueDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquitySecuritiesByIndustryAxis" xlink:label="us-gaap_EquitySecuritiesByIndustryAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquitySecuritiesIndustryMember" xlink:label="us-gaap_EquitySecuritiesIndustryMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfInvestmentsAtFairValue" xlink:label="ck0001925309_PercentageOfInvestmentsAtFairValue"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BusinessServicesMember" xlink:label="ck0001925309_BusinessServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ChemicalsMember" xlink:label="ck0001925309_ChemicalsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_CommunicationsMember" xlink:label="ck0001925309_CommunicationsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EducationMember" xlink:label="ck0001925309_EducationMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialServicesSectorMember" xlink:label="us-gaap_FinancialServicesSectorMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HealthcareSectorMember" xlink:label="us-gaap_HealthcareSectorMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_HotelGamingAndLeisureMember" xlink:label="ck0001925309_HotelGamingAndLeisureMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_HumanResourceSupportServicesMember" xlink:label="ck0001925309_HumanResourceSupportServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InsuranceMember" xlink:label="ck0001925309_InsuranceMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InternetServicesMember" xlink:label="ck0001925309_InternetServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ManufacturingMember" xlink:label="ck0001925309_ManufacturingMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_MarketingServicesMember" xlink:label="ck0001925309_MarketingServicesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OfficeProductsMember" xlink:label="ck0001925309_OfficeProductsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OilGasAndConsumableFuelsMember" xlink:label="ck0001925309_OilGasAndConsumableFuelsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OtherMember" xlink:label="ck0001925309_OtherMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PharmaceuticalsMember" xlink:label="ck0001925309_PharmaceuticalsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RealEstateSectorMember" xlink:label="us-gaap_RealEstateSectorMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RetailAndConsumerProductsMember" xlink:label="ck0001925309_RetailAndConsumerProductsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TransportationMember" xlink:label="ck0001925309_TransportationMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_EquitySecuritiesByIndustryAxis" xlink:to="us-gaap_EquitySecuritiesIndustryMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:to="us-gaap_EquitySecuritiesByIndustryAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="ck0001925309_PercentageOfInvestmentsAtFairValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_BusinessServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_ChemicalsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_CommunicationsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_EducationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="us-gaap_FinancialServicesSectorMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="us-gaap_HealthcareSectorMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_HotelGamingAndLeisureMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_HumanResourceSupportServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_InsuranceMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_InternetServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_ManufacturingMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_MarketingServicesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_OfficeProductsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_OilGasAndConsumableFuelsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_OtherMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_PharmaceuticalsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="us-gaap_RealEstateSectorMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_RetailAndConsumerProductsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquitySecuritiesIndustryMember" xlink:to="ck0001925309_TransportationMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureInvestmentsAtFairValueSummaryOfGeographicCompositionOfInvestmentsAtFairValueDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2022/country-2022.xsd#country_US" xlink:label="country_US"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_MidwestMember" xlink:label="ck0001925309_MidwestMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfInvestmentsAtFairValue" xlink:label="ck0001925309_PercentageOfInvestmentsAtFairValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2022/country-2022.xsd#country_AU" xlink:label="country_AU"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NortheastMember" xlink:label="ck0001925309_NortheastMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2022/country-2022.xsd#country_DE" xlink:label="country_DE"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SouthMember" xlink:label="ck0001925309_SouthMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2022/country-2022.xsd#country_LU" xlink:label="country_LU"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_WestMember" xlink:label="ck0001925309_WestMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2022/country-2022.xsd#country_NO" xlink:label="country_NO"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2022/country-2022.xsd#country_BM" xlink:label="country_BM"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2022/country-2022.xsd#country_CA" xlink:label="country_CA"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_US" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:to="srt_StatementGeographicalAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="country_US" xlink:to="ck0001925309_MidwestMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="ck0001925309_PercentageOfInvestmentsAtFairValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_AU" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="country_US" xlink:to="ck0001925309_NortheastMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_DE" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="country_US" xlink:to="ck0001925309_SouthMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_LU" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="country_US" xlink:to="ck0001925309_WestMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_NO" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_BM" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_CA" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDerivativesSummaryOfAmountsPaidAndReceivedOnInterestRateSwapTransactionsExcludingUpfrontFeesDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeLineItems" xlink:label="us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeTable" xlink:label="us-gaap_DerivativeTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapOneMember" xlink:label="ck0001925309_InterestRateSwapOneMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeMaturityDates" xlink:label="us-gaap_DerivativeMaturityDates"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapTwoMember" xlink:label="ck0001925309_InterestRateSwapTwoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DerivativeNotionalAmountHeldDuringPeriod" xlink:label="ck0001925309_DerivativeNotionalAmountHeldDuringPeriod"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapThreeMember" xlink:label="ck0001925309_InterestRateSwapThreeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForHedgeInvestingActivities" xlink:label="us-gaap_PaymentsForHedgeInvestingActivities"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapFourMember" xlink:label="ck0001925309_InterestRateSwapFourMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromHedgeInvestingActivities" xlink:label="us-gaap_ProceedsFromHedgeInvestingActivities"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapFiveMember" xlink:label="ck0001925309_InterestRateSwapFiveMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForProceedsFromHedgeInvestingActivities" xlink:label="us-gaap_PaymentsForProceedsFromHedgeInvestingActivities"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapSixMember" xlink:label="ck0001925309_InterestRateSwapSixMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapSevenMember" xlink:label="ck0001925309_InterestRateSwapSevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapEightMember" xlink:label="ck0001925309_InterestRateSwapEightMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapNineMember" xlink:label="ck0001925309_InterestRateSwapNineMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapTenMember" xlink:label="ck0001925309_InterestRateSwapTenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapElevenMember" xlink:label="ck0001925309_InterestRateSwapElevenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapTwelveMember" xlink:label="ck0001925309_InterestRateSwapTwelveMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapThirteenMember" xlink:label="ck0001925309_InterestRateSwapThirteenMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InterestRateSwapFourteenMember" xlink:label="ck0001925309_InterestRateSwapFourteenMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DerivativeTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapOneMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DerivativeMaturityDates" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapTwoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="ck0001925309_DerivativeNotionalAmountHeldDuringPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapThreeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_PaymentsForHedgeInvestingActivities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapFourMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_ProceedsFromHedgeInvestingActivities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapFiveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_PaymentsForProceedsFromHedgeInvestingActivities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapSixMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapSevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapEightMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapNineMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapTenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapElevenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapTwelveMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapThirteenMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="ck0001925309_InterestRateSwapFourteenMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDerivativesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeLineItems" xlink:label="us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeTable" xlink:label="us-gaap_DerivativeTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusDomain" xlink:label="us-gaap_PledgedStatusDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetPledgedAsCollateralMember" xlink:label="us-gaap_AssetPledgedAsCollateralMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnrealizedGainLossOnDerivatives" xlink:label="us-gaap_UnrealizedGainLossOnDerivatives"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusAxis" xlink:label="us-gaap_PledgedStatusAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusDomain" xlink:label="us-gaap_PledgedStatusDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationAxis" xlink:label="us-gaap_HedgingDesignationAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NondesignatedMember" xlink:label="us-gaap_NondesignatedMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseMember" xlink:label="us-gaap_InterestExpenseMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwoThousandTwentyFourNotesMember" xlink:label="ck0001925309_TwoThousandTwentyFourNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentIncreaseDecreaseForPeriodNet" xlink:label="us-gaap_DebtInstrumentIncreaseDecreaseForPeriodNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DesignatedAsHedgingInstrumentMember" xlink:label="us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwoThousandTwentySixNotesMember" xlink:label="ck0001925309_TwoThousandTwentySixNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeFairValueOfDerivativeNet" xlink:label="us-gaap_DerivativeFairValueOfDerivativeNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Cash" xlink:label="us-gaap_Cash"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DerivativeTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PledgedStatusDomain" xlink:to="us-gaap_AssetPledgedAsCollateralMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateSwapMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_UnrealizedGainLossOnDerivatives" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PledgedStatusAxis" xlink:to="us-gaap_PledgedStatusDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PledgedStatusAxis" xlink:to="us-gaap_PledgedStatusDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_HedgingDesignationDomain" xlink:to="us-gaap_NondesignatedMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_InterestExpenseMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TwoThousandTwentyFourNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DebtInstrumentIncreaseDecreaseForPeriodNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_HedgingDesignationAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_HedgingDesignationDomain" xlink:to="us-gaap_DesignatedAsHedgingInstrumentMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TwoThousandTwentySixNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DerivativeFairValueOfDerivativeNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_IncomeStatementLocationAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_Cash" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_DebtInstrumentAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_PledgedStatusAxis" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsFairValueMeasurementsOfInvestmentsDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienDebtInvestmentsMember" xlink:label="ck0001925309_FirstLienDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TradingSecuritiesDebt" xlink:label="us-gaap_TradingSecuritiesDebt"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EquityAndOtherInvestments" xlink:label="ck0001925309_EquityAndOtherInvestments"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InvestmentsFairValueDisclosureNet" xlink:label="ck0001925309_InvestmentsFairValueDisclosureNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_FirstLienDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_TradingSecuritiesDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="ck0001925309_EquityAndOtherInvestments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="ck0001925309_InvestmentsFairValueDisclosureNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsChangesInFairValueOfInvestmentsUsingLevel3InputsDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienDebtInvestmentsMember" xlink:label="ck0001925309_FirstLienDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EquityAndOtherInvestmentsMember" xlink:label="ck0001925309_EquityAndOtherInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetRecurringBasisStillHeldUnrealizedGainLossStatementOfIncomeExtensibleList" xlink:label="us-gaap_FairValueAssetRecurringBasisStillHeldUnrealizedGainLossStatementOfIncomeExtensibleList"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetNetAmortizationOfDiscountOnInvestment" xlink:label="ck0001925309_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetNetAmortizationOfDiscountOnInvestment"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_FirstLienDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_EquityAndOtherInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueAssetRecurringBasisStillHeldUnrealizedGainLossStatementOfIncomeExtensibleList" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="ck0001925309_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetNetAmortizationOfDiscountOnInvestment" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsNetChangeInUnrealizedGainsOrLossesOnInvestmentsForWhichLevel3InputsWereUsedInDeterminingFairValueDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienDebtInvestmentsMember" xlink:label="ck0001925309_FirstLienDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss" xlink:label="us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_FirstLienDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsFairValueOfLevel3InvestmentsAtFairValueSignificantUnobservableInputsUsedInValuationsDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="us-gaap_ValuationTechniqueAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FirstLienDebtInvestmentsMember" xlink:label="ck0001925309_FirstLienDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AlternativeInvestment" xlink:label="us-gaap_AlternativeInvestment"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="us-gaap_ValuationTechniqueDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeApproachValuationTechniqueMember" xlink:label="us-gaap_IncomeApproachValuationTechniqueMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputDiscountRateMember" xlink:label="us-gaap_MeasurementInputDiscountRateMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="us-gaap_MeasurementInputTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="us-gaap_ValuationTechniqueDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecondLienDebtInvestmentsMember" xlink:label="ck0001925309_SecondLienDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AlternativeInvestmentMeasurementInput" xlink:label="us-gaap_AlternativeInvestmentMeasurementInput"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MarketApproachValuationTechniqueMember" xlink:label="us-gaap_MarketApproachValuationTechniqueMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputComparabilityAdjustmentMember" xlink:label="us-gaap_MeasurementInputComparabilityAdjustmentMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_MezzanineDebtInvestmentsMember" xlink:label="ck0001925309_MezzanineDebtInvestmentsMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_MeasurementInputTransactionValueMember" xlink:label="ck0001925309_MeasurementInputTransactionValueMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_WeightedAverageMember" xlink:label="srt_WeightedAverageMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostApproachValuationTechniqueMember" xlink:label="us-gaap_CostApproachValuationTechniqueMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EquityAndOtherInvestmentsMember" xlink:label="ck0001925309_EquityAndOtherInvestmentsMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_ValuationTechniqueAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_FirstLienDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_AlternativeInvestment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ValuationTechniqueDomain" xlink:to="us-gaap_IncomeApproachValuationTechniqueMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputDiscountRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_MeasurementInputTypeAxis" xlink:to="us-gaap_MeasurementInputTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_MeasurementInputTypeAxis" xlink:to="us-gaap_MeasurementInputTypeDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ValuationTechniqueAxis" xlink:to="us-gaap_ValuationTechniqueDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_ValuationTechniqueAxis" xlink:to="us-gaap_ValuationTechniqueDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_InvestmentTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_SecondLienDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_AlternativeInvestmentMeasurementInput" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ValuationTechniqueDomain" xlink:to="us-gaap_MarketApproachValuationTechniqueMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputComparabilityAdjustmentMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_MeasurementInputTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_MezzanineDebtInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ValuationTechniqueDomain" xlink:to="ck0001925309_MeasurementInputTransactionValueMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_WeightedAverageMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_CostApproachValuationTechniqueMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="ck0001925309_EquityAndOtherInvestmentsMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsFairValueOfFinancialInstrumentsFairValueOfNotesDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosureAssetAndLiabilityNotMeasuredAtFairValueLineItems" xlink:label="us-gaap_FairValueDisclosureAssetAndLiabilityNotMeasuredAtFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:label="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesPayable" xlink:label="us-gaap_NotesPayable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyTwentyTwoConvertibleNotesMember" xlink:label="ck0001925309_TwentyTwentyTwoConvertibleNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NotesPayableFairValueDisclosure" xlink:label="us-gaap_NotesPayableFairValueDisclosure"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyTwentyThreeNotesMember" xlink:label="ck0001925309_TwentyTwentyThreeNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyTwentyFourNotesMember" xlink:label="ck0001925309_TwentyTwentyFourNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwentyTwentySixNotesMember" xlink:label="ck0001925309_TwentyTwentySixNotesMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueDisclosureAssetAndLiabilityNotMeasuredAtFairValueLineItems" xlink:to="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTable" xlink:to="us-gaap_DebtInstrumentAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueDisclosureAssetAndLiabilityNotMeasuredAtFairValueLineItems" xlink:to="us-gaap_NotesPayable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TwentyTwentyTwoConvertibleNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueDisclosureAssetAndLiabilityNotMeasuredAtFairValueLineItems" xlink:to="us-gaap_NotesPayableFairValueDisclosure" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TwentyTwentyThreeNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TwentyTwentyFourNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TwentyTwentySixNotesMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDebtAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityAxis" xlink:label="us-gaap_CreditFacilityAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis" xlink:label="us-gaap_VariableRateAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain" xlink:label="us-gaap_VariableRateDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SubscriptionFacilityMember" xlink:label="ck0001925309_SubscriptionFacilityMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:label="us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AssetCoveragePercentage" xlink:label="ck0001925309_AssetCoveragePercentage"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="us-gaap_RevolvingCreditFacilityMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BaseRateMember" xlink:label="us-gaap_BaseRateMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="us-gaap_DebtInstrumentFaceAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LetterOfCreditMember" xlink:label="us-gaap_LetterOfCreditMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AdjustedDailySimpleSecuredOvernightFinancingMember" xlink:label="ck0001925309_AdjustedDailySimpleSecuredOvernightFinancingMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AdjustedTermSimpleSecuredOvernightFinancingMember" xlink:label="ck0001925309_AdjustedTermSimpleSecuredOvernightFinancingMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_LineOfCreditFacilityMaximumBorrowingCapacityUnderCertainCircumstances" xlink:label="ck0001925309_LineOfCreditFacilityMaximumBorrowingCapacityUnderCertainCircumstances"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PrimeRateMember" xlink:label="us-gaap_PrimeRateMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_LineOfCreditFacilityStatedMaturityDate" xlink:label="ck0001925309_LineOfCreditFacilityStatedMaturityDate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FederalFundsEffectiveSwapRateMember" xlink:label="us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OptionalExtensionPeriodOfMaturityDateOfLineOfCreditFacility" xlink:label="ck0001925309_OptionalExtensionPeriodOfMaturityDateOfLineOfCreditFacility"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EurodollarMember" xlink:label="us-gaap_EurodollarMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SterlingOvernightInterbankAverageRateMember" xlink:label="ck0001925309_SterlingOvernightInterbankAverageRateMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityExpirationDate1" xlink:label="us-gaap_LineOfCreditFacilityExpirationDate1"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SecuredOvernightFinancingRateMember" xlink:label="ck0001925309_SecuredOvernightFinancingRateMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_LineOfCreditFacilityAdditionalBorrowingCapacity" xlink:label="ck0001925309_LineOfCreditFacilityAdditionalBorrowingCapacity"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AlternativeBaseRateMember" xlink:label="ck0001925309_AlternativeBaseRateMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCredit" xlink:label="us-gaap_LineOfCredit"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SpecifiedRelevantRateMember" xlink:label="ck0001925309_SpecifiedRelevantRateMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage" xlink:label="us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt" xlink:label="us-gaap_LongTermDebt"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityInterestRateDuringPeriod" xlink:label="us-gaap_LineOfCreditFacilityInterestRateDuringPeriod"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd" xlink:label="us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" xlink:label="us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RatioOfIndebtednessToNetCapital1" xlink:label="us-gaap_RatioOfIndebtednessToNetCapital1"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfCoveredDebtAmount" xlink:label="ck0001925309_PercentageOfCoveredDebtAmount"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NumberOfConsecutiveBusinessDay" xlink:label="ck0001925309_NumberOfConsecutiveBusinessDay"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfAdjustedBorrowingBaseUnderCreditFacility" xlink:label="ck0001925309_PercentageOfAdjustedBorrowingBaseUnderCreditFacility"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PercentageOfNetProceedsOfSaleOfEquityInterests" xlink:label="ck0001925309_PercentageOfNetProceedsOfSaleOfEquityInterests"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AdditionalAggregatePrincipalAmount" xlink:label="ck0001925309_AdditionalAggregatePrincipalAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="us-gaap_DebtInstrumentMaturityDate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:label="us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ExtinguishmentOfDebtAmount" xlink:label="us-gaap_ExtinguishmentOfDebtAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:label="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConvertibleNotesPayable" xlink:label="us-gaap_ConvertibleNotesPayable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtConversionConvertedInstrumentAmount1" xlink:label="us-gaap_DebtConversionConvertedInstrumentAmount1"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DebtInstrumentInitialConversionRate" xlink:label="ck0001925309_DebtInstrumentInitialConversionRate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtConversionConvertedInstrumentSharesIssued1" xlink:label="us-gaap_DebtConversionConvertedInstrumentSharesIssued1"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DebtConversionPrincipalAmount" xlink:label="ck0001925309_DebtConversionPrincipalAmount"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ProceedsFromSettlementsOfInterestRateSwapsExcludingUpfrontFees" xlink:label="ck0001925309_ProceedsFromSettlementsOfInterestRateSwapsExcludingUpfrontFees"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PaymentsForSettlementsOfInterestRateSwapsExcludingUpfrontFees" xlink:label="ck0001925309_PaymentsForSettlementsOfInterestRateSwapsExcludingUpfrontFees"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ProceedsFromSettlementsOfInterestRateSwapsRelatedToConvertibleNotes" xlink:label="ck0001925309_ProceedsFromSettlementsOfInterestRateSwapsRelatedToConvertibleNotes"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PaymentsForSettlementsOfInterestRateSwapsRelatedToConvertibleNotes" xlink:label="ck0001925309_PaymentsForSettlementsOfInterestRateSwapsRelatedToConvertibleNotes"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromUnsecuredNotesPayable" xlink:label="us-gaap_ProceedsFromUnsecuredNotesPayable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeNotionalAmount" xlink:label="us-gaap_DerivativeNotionalAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeMaturityDates" xlink:label="us-gaap_DerivativeMaturityDates"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeFairValueHedgeIncludedInEffectivenessGainLoss" xlink:label="us-gaap_DerivativeFairValueHedgeIncludedInEffectivenessGainLoss"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnFairValueHedgeIneffectivenessNet" xlink:label="us-gaap_GainLossOnFairValueHedgeIneffectivenessNet"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DebtInstrumentCovenantMinimumConsolidatedAssetsLessSecuredDebt" xlink:label="ck0001925309_DebtInstrumentCovenantMinimumConsolidatedAssetsLessSecuredDebt"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays" xlink:label="us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1" xlink:label="us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger" xlink:label="us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DebtInstrumentConvertibleBusinessDayPeriod" xlink:label="ck0001925309_DebtInstrumentConvertibleBusinessDayPeriod"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DebtInstrumentConvertibleMeasurementPeriodConsecutiveTradingDays" xlink:label="ck0001925309_DebtInstrumentConvertibleMeasurementPeriodConsecutiveTradingDays"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DebtInstrumentConvertibleMeasurementPeriodThresholdPercentageOfTradingPrice" xlink:label="ck0001925309_DebtInstrumentConvertibleMeasurementPeriodThresholdPercentageOfTradingPrice"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_CreditFacilityAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_VariableRateAxis" xlink:to="us-gaap_VariableRateDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="ck0001925309_SubscriptionFacilityMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_LondonInterbankOfferedRateLIBORMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_AssetCoveragePercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_RevolvingCreditFacilityMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_BaseRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentFaceAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_VariableRateAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_LetterOfCreditMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_AdjustedDailySimpleSecuredOvernightFinancingMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_SubsequentEventTypeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_AdjustedTermSimpleSecuredOvernightFinancingMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_LineOfCreditFacilityMaximumBorrowingCapacityUnderCertainCircumstances" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_PrimeRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_LineOfCreditFacilityStatedMaturityDate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_FederalFundsEffectiveSwapRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_OptionalExtensionPeriodOfMaturityDateOfLineOfCreditFacility" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_EurodollarMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_SterlingOvernightInterbankAverageRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityExpirationDate1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_SecuredOvernightFinancingRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_LineOfCreditFacilityAdditionalBorrowingCapacity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_AlternativeBaseRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCredit" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="ck0001925309_SpecifiedRelevantRateMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityCommitmentFeePercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LongTermDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LettersOfCreditOutstandingAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityInterestRateDuringPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_RatioOfIndebtednessToNetCapital1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_PercentageOfCoveredDebtAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_NumberOfConsecutiveBusinessDay" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_PercentageOfAdjustedBorrowingBaseUnderCreditFacility" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_StockholdersEquity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_PercentageOfNetProceedsOfSaleOfEquityInterests" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_AdditionalAggregatePrincipalAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentMaturityDate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentConvertibleConversionPrice1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="26" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_ExtinguishmentOfDebtAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="27" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_GainsLossesOnExtinguishmentOfDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="28" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="29" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="30" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_ConvertibleNotesPayable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="31" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtConversionConvertedInstrumentAmount1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="32" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_DebtInstrumentInitialConversionRate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="33" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtConversionConvertedInstrumentSharesIssued1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="34" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_DebtConversionPrincipalAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="35" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_ProceedsFromSettlementsOfInterestRateSwapsExcludingUpfrontFees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="36" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_PaymentsForSettlementsOfInterestRateSwapsExcludingUpfrontFees" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="37" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_ProceedsFromSettlementsOfInterestRateSwapsRelatedToConvertibleNotes" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="38" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_PaymentsForSettlementsOfInterestRateSwapsRelatedToConvertibleNotes" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="39" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_ProceedsFromUnsecuredNotesPayable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="40" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DerivativeNotionalAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="41" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DerivativeMaturityDates" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="42" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DerivativeFairValueHedgeIncludedInEffectivenessGainLoss" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="43" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_GainLossOnFairValueHedgeIneffectivenessNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="44" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_DebtInstrumentCovenantMinimumConsolidatedAssetsLessSecuredDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="45" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentConvertibleThresholdTradingDays" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="46" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="47" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="48" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_DebtInstrumentConvertibleBusinessDayPeriod" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="49" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_DebtInstrumentConvertibleMeasurementPeriodConsecutiveTradingDays" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="50" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="ck0001925309_DebtInstrumentConvertibleMeasurementPeriodThresholdPercentageOfTradingPrice" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDebtScheduleOfDebtObligationsDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityAxis" xlink:label="us-gaap_CreditFacilityAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SubscriptionFacilityMember" xlink:label="ck0001925309_SubscriptionFacilityMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="us-gaap_DebtInstrumentFaceAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentCarryingAmount" xlink:label="us-gaap_DebtInstrumentCarryingAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt" xlink:label="us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_CreditFacilityAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="ck0001925309_SubscriptionFacilityMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentFaceAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentCarryingAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LongTermDebt" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/DisclosureDebtScheduleOfDebtObligationsParentheticalDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityAxis" xlink:label="us-gaap_CreditFacilityAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SubscriptionFacilityMember" xlink:label="ck0001925309_SubscriptionFacilityMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsNet" xlink:label="us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_CreditFacilityAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="ck0001925309_SubscriptionFacilityMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DeferredFinanceCostsNet" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureDebtScheduleOfComponentsOfInterestExpenseDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseDebt" xlink:label="us-gaap_InterestExpenseDebt"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtRelatedCommitmentFeesAndDebtIssuanceCosts" xlink:label="us-gaap_DebtRelatedCommitmentFeesAndDebtIssuanceCosts"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfFinancingCosts" xlink:label="us-gaap_AmortizationOfFinancingCosts"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestAndDebtExpense" xlink:label="us-gaap_InterestAndDebtExpense"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityAverageOutstandingAmount" xlink:label="us-gaap_LineOfCreditFacilityAverageOutstandingAmount"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtWeightedAverageInterestRateOverTime" xlink:label="us-gaap_LongTermDebtWeightedAverageInterestRateOverTime"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_InterestExpenseDebt" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtRelatedCommitmentFeesAndDebtIssuanceCosts" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_AmortizationOfFinancingCosts" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_InterestAndDebtExpense" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LineOfCreditFacilityAverageOutstandingAmount" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LongTermDebtWeightedAverageInterestRateOverTime" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesScheduleOfCommitmentsToFundInvestmentsInCurrentPortfolioCompaniesDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesLineItems" xlink:label="us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesTable" xlink:label="us-gaap_LossContingenciesTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_RevolverMember" xlink:label="ck0001925309_RevolverMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AlphaMidcoIncMember" xlink:label="ck0001925309_AlphaMidcoIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PurchaseCommitmentToFundInvestment" xlink:label="ck0001925309_PurchaseCommitmentToFundInvestment"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DelayedDrawAndRevolverMember" xlink:label="ck0001925309_DelayedDrawAndRevolverMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AmericanAchievementCorpMember" xlink:label="ck0001925309_AmericanAchievementCorpMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DelayedDrawMember" xlink:label="ck0001925309_DelayedDrawMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AvidXchangeIncMember" xlink:label="ck0001925309_AvidXchangeIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DelayedDrawConvertibleNoteMember" xlink:label="ck0001925309_DelayedDrawConvertibleNoteMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AxonifyIncMember" xlink:label="ck0001925309_AxonifyIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AvalaraIncMember" xlink:label="ck0001925309_AvalaraIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BayshoreIntermediate2LPMember" xlink:label="ck0001925309_BayshoreIntermediate2LPMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BiohavenPharmaceuticalsIncMember" xlink:label="ck0001925309_BiohavenPharmaceuticalsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BlueSnapIncMember" xlink:label="ck0001925309_BlueSnapIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_BtrsHoldingIncMember" xlink:label="ck0001925309_BtrsHoldingIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ClinicientIncMember" xlink:label="ck0001925309_ClinicientIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DaySmartHoldingsLLCMember" xlink:label="ck0001925309_DaySmartHoldingsLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DestinySolutionsParentHoldingCompanyMember" xlink:label="ck0001925309_DestinySolutionsParentHoldingCompanyMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DyeDurhamCorpMember" xlink:label="ck0001925309_DyeDurhamCorpMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EmploymentHeroHoldingsPtyLtdMember" xlink:label="ck0001925309_EmploymentHeroHoldingsPtyLtdMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EMSLinqIncMember" xlink:label="ck0001925309_EMSLinqIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ExtraHopNetworksIncMember" xlink:label="ck0001925309_ExtraHopNetworksIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ErlingLuxBidcoSarlMember" xlink:label="ck0001925309_ErlingLuxBidcoSarlMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_FactorSystemsIncMember" xlink:label="ck0001925309_FactorSystemsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ForeScoutTechnologiesIncMember" xlink:label="ck0001925309_ForeScoutTechnologiesIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_GTreasurySSLLCMember" xlink:label="ck0001925309_GTreasurySSLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_HornetsecurityHoldingGmbhMember" xlink:label="ck0001925309_HornetsecurityHoldingGmbhMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IbisIntermediateCoMember" xlink:label="ck0001925309_IbisIntermediateCoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IntegrationApplianceIncMember" xlink:label="ck0001925309_IntegrationApplianceIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IntelePeerHoldingsIncMember" xlink:label="ck0001925309_IntelePeerHoldingsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InvmetricsHoldingsIncMember" xlink:label="ck0001925309_InvmetricsHoldingsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IRGSEHoldingCorpMember" xlink:label="ck0001925309_IRGSEHoldingCorpMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_KyribaCorpMember" xlink:label="ck0001925309_KyribaCorpMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_LexipolLlcMember" xlink:label="ck0001925309_LexipolLlcMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_LithiumTechnologiesLLCMember" xlink:label="ck0001925309_LithiumTechnologiesLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_LucidworksIncMember" xlink:label="ck0001925309_LucidworksIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NetwrixCorpMember" xlink:label="ck0001925309_NetwrixCorpMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NeuintelLLCMember" xlink:label="ck0001925309_NeuintelLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NintexGlobalLtdMember" xlink:label="ck0001925309_NintexGlobalLtdMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OutsystemsLuxcoMember" xlink:label="ck0001925309_OutsystemsLuxcoMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_OutsystemsLuxcoSarlMember" xlink:label="ck0001925309_OutsystemsLuxcoSarlMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PageUpPeopleLtdMember" xlink:label="ck0001925309_PageUpPeopleLtdMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PassportLabsIncMember" xlink:label="ck0001925309_PassportLabsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PayScaleHoldingsIncMember" xlink:label="ck0001925309_PayScaleHoldingsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PrimePayIntermediateLLCMember" xlink:label="ck0001925309_PrimePayIntermediateLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PingIdentityCorporationMember" xlink:label="ck0001925309_PingIdentityCorporationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PingIdentityHoldingCorporationMember" xlink:label="ck0001925309_PingIdentityHoldingCorporationMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_PrimeRevenueIncMember" xlink:label="ck0001925309_PrimeRevenueIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_Project44IncMember" xlink:label="ck0001925309_Project44IncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ReliaQuestHoldingsLLCMember" xlink:label="ck0001925309_ReliaQuestHoldingsLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ResmanLlcMember" xlink:label="ck0001925309_ResmanLlcMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_SprinklrIncMember" xlink:label="ck0001925309_SprinklrIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TangoManagementConsultingLLCMember" xlink:label="ck0001925309_TangoManagementConsultingLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TRPAssetsLLCMember" xlink:label="ck0001925309_TRPAssetsLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_ValantMedicalSolutionsIncMember" xlink:label="ck0001925309_ValantMedicalSolutionsIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_VerdadResourcesIntermediateHoldingsLLCMember" xlink:label="ck0001925309_VerdadResourcesIntermediateHoldingsLLCMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_WideOrbitIncMember" xlink:label="ck0001925309_WideOrbitIncMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_WorkwellAcquisitionCoMember" xlink:label="ck0001925309_WorkwellAcquisitionCoMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="us-gaap_LossContingenciesTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ck0001925309_RevolverMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_AlphaMidcoIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="ck0001925309_PurchaseCommitmentToFundInvestment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_LossContingenciesTable" xlink:to="us-gaap_FinancialInstrumentAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ck0001925309_DelayedDrawAndRevolverMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_AmericanAchievementCorpMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_LossContingenciesTable" xlink:to="srt_ConsolidatedEntitiesAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ck0001925309_DelayedDrawMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_AvidXchangeIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="ck0001925309_DelayedDrawConvertibleNoteMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_AxonifyIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_AvalaraIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_BayshoreIntermediate2LPMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_BiohavenPharmaceuticalsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_BlueSnapIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_BtrsHoldingIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_ClinicientIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_DaySmartHoldingsLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_DestinySolutionsParentHoldingCompanyMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_DyeDurhamCorpMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_EmploymentHeroHoldingsPtyLtdMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_EMSLinqIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="15" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_ExtraHopNetworksIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="16" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_ErlingLuxBidcoSarlMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="17" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_FactorSystemsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="18" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_ForeScoutTechnologiesIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="19" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_GTreasurySSLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="20" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_HornetsecurityHoldingGmbhMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="21" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_IbisIntermediateCoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="22" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_IntegrationApplianceIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="23" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_IntelePeerHoldingsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="24" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_InvmetricsHoldingsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="25" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_IRGSEHoldingCorpMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="26" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_KyribaCorpMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="27" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_LexipolLlcMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="28" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_LithiumTechnologiesLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="29" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_LucidworksIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="30" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_NetwrixCorpMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="31" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_NeuintelLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="32" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_NintexGlobalLtdMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="33" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_OutsystemsLuxcoMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="34" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_OutsystemsLuxcoSarlMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="35" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_PageUpPeopleLtdMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="36" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_PassportLabsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="37" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_PayScaleHoldingsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="38" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_PrimePayIntermediateLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="39" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_PingIdentityCorporationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="40" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_PingIdentityHoldingCorporationMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="41" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_PrimeRevenueIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="42" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_Project44IncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="43" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_ReliaQuestHoldingsLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="44" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_ResmanLlcMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="45" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_SprinklrIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="46" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_TangoManagementConsultingLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="47" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_TRPAssetsLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="48" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_ValantMedicalSolutionsIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="49" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_VerdadResourcesIntermediateHoldingsLLCMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="50" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_WideOrbitIncMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="51" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="ck0001925309_WorkwellAcquisitionCoMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesLineItems" xlink:label="us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesTable" xlink:label="us-gaap_LossContingenciesTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherCommitment" xlink:label="us-gaap_OtherCommitment"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnfundedLoanCommitmentMember" xlink:label="us-gaap_UnfundedLoanCommitmentMember"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="us-gaap_LossContingenciesTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="us-gaap_OtherCommitment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_LossContingenciesTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_UnfundedLoanCommitmentMember" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/Role_DisclosureNetAssetsAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockLineItems" xlink:label="us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="us-gaap_ScheduleOfStockByClassTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OverAllotmentOptionMember" xlink:label="us-gaap_OverAllotmentOptionMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_default"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="us-gaap_RelatedPartyTransactionAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="us-gaap_RelatedPartyTransactionDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_AdviserMember" xlink:label="ck0001925309_AdviserMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TwoThousandTwentyTwoConvertibleNotesMember" xlink:label="ck0001925309_TwoThousandTwentyTwoConvertibleNotesMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_CapitalCommitmentReceivedFormInvestors" xlink:label="ck0001925309_CapitalCommitmentReceivedFormInvestors"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_CapitalCommitmentsRemainingUndrawn" xlink:label="ck0001925309_CapitalCommitmentsRemainingUndrawn"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:label="us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtConversionOriginalDebtAmount1" xlink:label="us-gaap_DebtConversionOriginalDebtAmount1"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_CurrentMarketPricePerSharePercentage" xlink:label="ck0001925309_CurrentMarketPricePerSharePercentage"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount1" xlink:label="us-gaap_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchaseProgramPeriodInForce1" xlink:label="us-gaap_StockRepurchaseProgramPeriodInForce1"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchaseProgramExpirationDate" xlink:label="us-gaap_StockRepurchaseProgramExpirationDate"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockSharesAcquired" xlink:label="us-gaap_TreasuryStockSharesAcquired"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockAcquiredAverageCostPerShare" xlink:label="us-gaap_TreasuryStockAcquiredAverageCostPerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ScheduleOfStockByClassTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_OverAllotmentOptionMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_default" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_RelatedPartyTransactionAxis" xlink:to="us-gaap_RelatedPartyTransactionDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_DebtInstrumentAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyTransactionDomain" xlink:to="ck0001925309_AdviserMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="ck0001925309_TwoThousandTwentyTwoConvertibleNotesMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_RelatedPartyTransactionAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_CommonStockSharesIssued" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_SharesIssuedPricePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="ck0001925309_CapitalCommitmentReceivedFormInvestors" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="ck0001925309_CapitalCommitmentsRemainingUndrawn" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_DebtConversionOriginalDebtAmount1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="ck0001925309_CurrentMarketPricePerSharePercentage" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockRepurchaseProgramAuthorizedAmount1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockRepurchaseProgramPeriodInForce1" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_StockRepurchaseProgramExpirationDate" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_TreasuryStockSharesAcquired" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="13" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_TreasuryStockAcquiredAverageCostPerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="14" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_TreasuryStockValueAcquiredCostMethod" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TaxCreditCarryforwardLineItems" xlink:label="us-gaap_TaxCreditCarryforwardLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TaxCreditCarryforwardTable" xlink:label="us-gaap_TaxCreditCarryforwardTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IncreaseDecreaseInDistributableEarnings" xlink:label="ck0001925309_IncreaseDecreaseInDistributableEarnings"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_IncreaseDecreaseInAdditionalPaidInCapital" xlink:label="ck0001925309_IncreaseDecreaseInAdditionalPaidInCapital"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_DeferredTaxLiabilityPertainingToUnrealizedGainsRelatedToInvestments" xlink:label="ck0001925309_DeferredTaxLiabilityPertainingToUnrealizedGainsRelatedToInvestments"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNet" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNet"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="us-gaap_OperatingLossCarryforwards"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_NumberOfInvestments" xlink:label="ck0001925309_NumberOfInvestments"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsGross" xlink:label="us-gaap_DeferredTaxAssetsGross"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsNet" xlink:label="us-gaap_DeferredTaxAssetsNet"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TaxCostOfInvestments" xlink:label="ck0001925309_TaxCostOfInvestments"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EstimatedGrossUnrealizedGainsOnTaxCostInvestment" xlink:label="ck0001925309_EstimatedGrossUnrealizedGainsOnTaxCostInvestment"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_EstimatedGrossUnrealizedLossOnTaxCostInvestment" xlink:label="ck0001925309_EstimatedGrossUnrealizedLossOnTaxCostInvestment"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ExciseAndSalesTaxes" xlink:label="us-gaap_ExciseAndSalesTaxes"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="us-gaap_TaxCreditCarryforwardTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_TaxCreditCarryforwardTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="ck0001925309_IncreaseDecreaseInDistributableEarnings" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="ck0001925309_IncreaseDecreaseInAdditionalPaidInCapital" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="ck0001925309_DeferredTaxLiabilityPertainingToUnrealizedGainsRelatedToInvestments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="us-gaap_DeferredTaxAssetsLiabilitiesNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="us-gaap_OperatingLossCarryforwards" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="ck0001925309_NumberOfInvestments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="6" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="us-gaap_DeferredTaxAssetsGross" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="us-gaap_DeferredTaxAssetsNet" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="ck0001925309_TaxCostOfInvestments" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="ck0001925309_EstimatedGrossUnrealizedGainsOnTaxCostInvestment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="ck0001925309_EstimatedGrossUnrealizedLossOnTaxCostInvestment" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TaxCreditCarryforwardLineItems" xlink:to="us-gaap_ExciseAndSalesTaxes" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://sixthstreet.com/20221231/taxonomy/role/DisclosureFinancialHighlightsSummaryOfFinancialHighlightsForOneShareCommonStockOutstandingDetails">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:label="us-gaap_InvestmentCompanyFinancialHighlightsLineItems"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyFinancialHighlightsTable" xlink:label="us-gaap_InvestmentCompanyFinancialHighlightsTable"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetAssetValuePerShare" xlink:label="us-gaap_NetAssetValuePerShare"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_WithoutManagementFeeWaiverMember" xlink:label="ck0001925309_WithoutManagementFeeWaiverMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyInvestmentIncomeLossPerShare" xlink:label="us-gaap_InvestmentCompanyInvestmentIncomeLossPerShare"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_WithManagementFeeWaiverMember" xlink:label="ck0001925309_WithManagementFeeWaiverMember"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyGainLossOnInvestmentPerShare" xlink:label="us-gaap_InvestmentCompanyGainLossOnInvestmentPerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyInvestmentIncomeLossFromOperationsPerShare" xlink:label="us-gaap_InvestmentCompanyInvestmentIncomeLossFromOperationsPerShare"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_InvestmentCompanyNetCommonShareIssuancePerShare" xlink:label="ck0001925309_InvestmentCompanyNetCommonShareIssuancePerShare"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyNetAssetValuePerSharePeriodIncreaseDecrease" xlink:label="us-gaap_InvestmentCompanyNetAssetValuePerSharePeriodIncreaseDecrease"/>
    <link:loc xlink:type="locator" xlink:href="ck0001925309-20221231.xsd#ck0001925309_TotalReturnBasedOnNetAssetValue" xlink:label="ck0001925309_TotalReturnBasedOnNetAssetValue"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyExpenseRatioBeforeIncentiveAllocation" xlink:label="us-gaap_InvestmentCompanyExpenseRatioBeforeIncentiveAllocation"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyInvestmentIncomeLossRatio" xlink:label="us-gaap_InvestmentCompanyInvestmentIncomeLossRatio"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentCompanyIncentiveFeeToAverageNetAssets" xlink:label="us-gaap_InvestmentCompanyIncentiveFeeToAverageNetAssets"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueNetAssetLiability" xlink:label="us-gaap_FairValueNetAssetLiability"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_InvestmentCompanyFinancialHighlightsTable" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsTable" xlink:to="us-gaap_IncomeStatementLocationAxis" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_NetAssetValuePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="ck0001925309_WithoutManagementFeeWaiverMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_InvestmentCompanyInvestmentIncomeLossPerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="1" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="ck0001925309_WithManagementFeeWaiverMember" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="2" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_InvestmentCompanyGainLossOnInvestmentPerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="3" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_InvestmentCompanyInvestmentIncomeLossFromOperationsPerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="4" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="ck0001925309_InvestmentCompanyNetCommonShareIssuancePerShare" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="5" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_InvestmentCompanyNetAssetValuePerSharePeriodIncreaseDecrease" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="7" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="ck0001925309_TotalReturnBasedOnNetAssetValue" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="8" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_CommonStockSharesOutstanding" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="9" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_InvestmentCompanyExpenseRatioBeforeIncentiveAllocation" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="10" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_InvestmentCompanyInvestmentIncomeLossRatio" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="11" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_InvestmentCompanyIncentiveFeeToAverageNetAssets" priority="2" use="optional"/>
    <link:definitionArc xlink:type="arc" order="12" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentCompanyFinancialHighlightsLineItems" xlink:to="us-gaap_FairValueNetAssetLiability" priority="2" use="optional"/>
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementAbstract" xlink:label="us-gaap_IncomeStatementAbstract"/>
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnrealizedGainLossOnInvestments" xlink:label="us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:type="arc" order="0" xbrldt:closed="false" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementAbstract" xlink:to="us-gaap_UnrealizedGainLossOnInvestments" priority="2" use="optional"/>
  </link:definitionLink>
</link:linkbase>
