I Thess 4:3-6 mentions that engaging in sexual activity outside of marriage is wronging someone, and taking advantage of them.
Barbara Wilson talks more on this:
When God says we sin against ourselves, He means that everything sexually wrong that we’ve done to the other person, we’ve also done to ourselves. The Thessalonians passage says that when we use someone sexually outside of marriage, we are wronging them and taking advantage of them. In some translations (KJV, NASB) the word for “taking advantage” is translated “defrauding.” To defraud is to rob someone of something.
Of what is someone robbed in sexual sin?
Ultimately, they are robbed of a special God-given gift that is meant for one person — their future spouse.. But additionally, they are robbed of the true love and intimacy that goes along with that gift in marriage. They’re robbed of intimacy with God, of human dignity, of trust and the ability to bond with one person for life. They’re robbed of saving sexual desire and arousal for their future spouse. They’re robbed of an unattached and pure mind, body, soul, and spirit.
And if we go a step further, we realize that the person’s future spouse is robbed of all these treasures as well.
Why does sexual sin hurt us so much? Because the very first time we engage in sex outside God’s plan — in that precise moment our eyes are opened. Sex is no longer a curious mystery or a desire yet to be satisfied. In an instant our hearts know that this is indeed something special, something holy, and something divine.
And something lost.
We’ve taken a valuable treasure from the other person. And we’ve also robbed ourselves. We now know that we’ve cheated ourselves of something that can never be replaced, and the remorse, the regret, the pain settle deep into our souls.
How could something that God created as holy, pure, and precious become so shameful, cheap, and misused? Satan took what God designed for our good and used it against us. Because sex involves the whole person — spirit, emotions, mind, and body — its abuse causes comprehensive damage. But the greatest impact of sexual sin is relational.
What a shrewd plan. What better way to keep people from drawing closer to God than to keep them from trusting people? And if I can’t trust you, whom I see, then I most certainly can’t trust a God that I can’t see.
Barbara Wilson, The Invisible Bond