If he thinks adultery didn't end his marriage, he's living in the deepest denial in human history. Yes, there are crackpot anthropologists who like to pretend that there are viable alternatives in the man-woman relationship. But you can find researchers who will use all kinds of bad science to prove their own pet theories. You cannot commit yourself to come home every day to the same woman if you're banging some other cutie. Eventually, inevitably, inexorably, the dynamic of one relationship winds down as the other spins up.
Sex is the fulcrum on which a heterosexual relationship is balanced.
Screw it up and the balance is lost. Any man married more than 10 years can tell you that. I might have believed you if you had even once granted that there was an element of pure, selfish desire to get your rocks off as much as possible. But no, according to you, every sexual encounter was part of an existential quest to define yourself and test boundaries. Or something like that.