In the Harry Potter series, the villain Voldemort, longing for immortality, breaks his soul into seven pieces. He believes that if he can split his soul into seven objects, even if one part is destroyed, the other parts will live on. But the consequence of creating a Horocrux was unspeakable. A fractured soul is an un-whole self, broken beyond comprehension. In Albus Dumbledore’s words, Voldemort was a “maimed and diminished soul.”
Sexual sin offers a similar lie to us. Sexual temptation suggests that fidelity won’t satisfy. If one sexual partner is good, more partners will be better. Why not experience pleasure with multiple partners? Think of what you are missing out on. Consider what that one partner doesn’t give you. Or, if you’re not married, how do you know you will ever be married? What does it hurt to fast forward that pleasure to now?