"Why are cheating wives so popular? You'd expect that would not be something men would like to think about.
It's one of the top interests all around the world. Men are wired to be sexually jealous. And, certainly, men can fly into murderous rages, but simultaneously they're also sexually aroused.
This is an example of what biologists call a sperm competition cue. Across the animal kingdom, when males see other males mating, it tends to provoke arousal. If he is going to compete with the other male, he has to produce more sperm
Human men also respond like this, if a man sees a woman — including his partner — with another man, he becomes more aroused."