I am always on awe about how completely sexualized a man's thoughts are, so much so that literally anything and everything can be sexualized if it hasn't been already. The whole cuckold dynamic is one example. Something like cheating, which should be an anathema to a healthy relationship and should "naturally" turn men off, has become a paraphilia for many of them.
Whenever women get cheated on it's always heartbreak, or at best indifference. But here are men who get TURNED ON by it, and even pressure their partners to cheat for their own sexual gratification.

Less and less I believe that rationalizations for their specific fetishes are based on truths. The only truth is that having over-sexed brains is the "natural" state of your average man. How he expresses it is the only thing that differentiates him from other men.