I’m supposing the thread is only focused on male cheaters, but we all know that women cheat too!
But back to the subject, I think that some men are addicted (not to sex) to the RUSH of emotions that you feel in a NEW relationship.
You know that feeling that you get when you are first falling in love and anything/everything seems possible. That “I feel great about you”, “I feel great about us”, and “We can make magic together” feelings.