Unfortunately, you probably won't find it in the Prayer Book anytime soon, but this collect by Julian Mann, a.k.a. Cranmer's Curate, is a healthy dose of biblical truth for a society that fantasizes about the church blessing sexual abominations.
Almighty and eternal God, who through your servant the Apostle Paul has taught Christian people to flee sexual immorality, we ask that you would give all of us who profess the faith of Christ grace to be obedient to your word. If we have chosen to have sexual relations outside the honourable estate of holy matrimony between one man and one woman for life, give us, we pray, the grace of repentance. Empower us, we beseech you, by your life-giving Holy Spirit to exercise self-control and to honour you with our bodies, through Jesus Christ your eternal Son our Lord.