More happens during sex than just a momentary experience of pleasure. When we are intimate, chemicals are released in our brains that bond us together. Vasopressin is primarily released in male brains and oxytocin primarily in females. However, when we bond then break, bond then break, we damage our capacity to bond strongly to the next person. It’s similar to how sticky a piece of tape is. The first time you apply it to a surface, it bonds strongly. But if you take it off and apply it to another surface, it’s less adhesive. Soon, it’s barely sticky at all.