Regardless of who's involved, people absolutely love to come up with convenient theories as to why people cheat. Men do it because they can, as the story goes, as though it's inconceivable to think that a man could be in an emotionally unfulfilling relationship. Women do it because the relationship has died, since apparently women are incapable of having ravenous sexual appetites. For either gender, maybe the cheater wants to know they've "still got it," or are drunk with power, either their own or someone else's. Convenient as these explanations may be, they're superficial and miss the larger point.
Cheating is about one thing, and that's the transgressor's inability or unwillingness to reconcile the feeling of love with the decision to love. Feeling love is easy, because it's a largely chemical affair. Everyone felt it in tidal waves when they were younger and experienced their "first love." As we get older, and our bodies calm down and feelings cease to be as new, we feel it less, but we still do.
You've felt love-type feelings for anyone you've ever dated on even a somewhat consistent basis. Those feelings are great, and they're what bring us together. But, once we cross that bridge into a serious, committed monogamous relationship, those feelings aren't enough. It's not exactly an intellectual exercise, but crossing that bridge still involves decision making and a full understanding of the implications of that decision. It's being able to say "OK, I've grown to love you such that I'm going to make this commitment to you, and I'm well aware of everything that commitment entails."
Someone who cheats, regardless of their stated reason, is someone who disregards the implications of that decision, or at best is never able to internalize them. When these things happen and couples attempt to reconcile, it's always something like, "Well, my trust is shattered but we love each other, so we're going to work past this." Well, of course you love each other -- that's why you're together in the first place. The difference is, is your cheating significant other now prepared to understand what it means to actively, intentionally love you? If so, why now? Why did betraying you result in that epiphany? Chances are, it did not. At best you've exposed the issues that made that kind of contractual love a farce, and at worst you're dealing with someone who, for whatever reason, was never able to reach that conclusion with you in the first place.
If you've been cheated on, there's no reason to cling to something that never was in hopes of salvaging your now-broken trust, because there are plenty of people out there who, eventually, will be willing to do what it takes. Similarly, if you're thinking you might end up a cheater yourself, why bother upholding the delusions of both you and your partner? Sometimes things don't work out, and that's OK. That's why we have things like divorce and breakup texts. Maybe your life circumstances have changed, and now you're no longer ready to make good on your commitment. Get out while you both have your dignity, and maybe do some soul searching as to why you were unable to choose to turn your feelings for this person into something more. Maybe it was just you, or maybe it was them. Either way, it's better than the alternative.
Or, just go through with it, and in no time you'll be a poll-leading political candidate for a major city.