I don't cheat. I am against it. But the guys that cheat cheat for the same reason women cheat. When a person cheats, man or woman they do it because something is missing in their current relationship so they look for someone else to provide them with what is missing.
Can you honestly say they're cheating versus living out the amount of commitment they actually have in the relationship?
Even Jesus said, "“You have heard that it was said, Do not commit adultery. But I tell you, everyone who looks at a woman to lust for her has already committed adultery with her in his heart."
You're worried about an outward action, but the act has already been committed long before that point. That's exactly why porn usage hurts people. Their body may be with someone but there heart is elsewhere.
So with that in mind, are you really sure they're cheating? Or did you just believe what they said or convinced yourself of their fidelity in the first place? When there was no proof or actions to back it up? There's a reason why so many people eventually admit they knew their partner wasn't faithful. But it takes time to admit that they just swept it under the rug and deluded themselves.
Monogamy is a social construct, not one based on our biology. Mormons believe in polygamy, so what you consider cheating is completely fine under the doctrines of Mormonism.
Guys cheat because they think it's worth the risk and don't care about personal integrity. Women cheat for the same reasons. Studies have shown that most people will cheat to a certain extent as long as they can get away with it, however we don't cheat when it diminishes our personal integrity.
Guys who cheat do it because they have the option to have sex with a different vagina and turning it down would be foolish. We don't do it because we don't care for our partners or are unhappy, we simply do it because it was offered. We don't attach emotions to it, we are getting off with a different vagina.
We definitely do NOT cheat for the same reasons as women. Women cheat because they are unhappy, are missing something from their relationship, are testing the waters to see if they really love their partner or not, are getting attention from a male who tells them things or gives them things which their partner doesn't. When women cheat, it's because they are looking for something else. It has emotional connection with it.
Same reason women do. They think they can get away with it