I'm quite interested in the black and whiteness of so many views expressed in this forum. I think what's most interesting is the tendency to condemn, as if behaving in a shitty way in one (admittedly central and vital) aspect of your life invalidates every other aspect. I was really struck by a couple of people claiming that a cheating partner cannot be called a good parent. I mean, of course a man who cheats is a bad partner, but the idea that this aspect of his behaviour invalidates his status as a good father (or a good anything) is ridiculous, and frankly pretty childish.
Nobody is all good. Very few people are all bad. Many people who have affairs know that it's a shitty thing to do, but they exist with that knowledge without it corrupting everything else, or being symptomatic of a wider moral failing. A person isn't trustworthy or untrustworthy, full stop: we are all trustworthy in some things, both big and small, and not in others. Everyone's frailties manifest in different ways; everyone makes different choices; everyone is a complex mess. We all live with compromised ethics in both big and small things, and we all have different values and attitudes to monogamy and infidelity and other vital, central things which change over time. I think it's important to remember that.
I am very wary of people who claim to have simple answers. People who don't recognise that we're all massively morally inconsistent don't really have any insights worth hearing. I think victims of infidelity on this forum constantly hear how their cheating partners are just scumbags, when the truth is that they're actually just normal people who've done a scummy thing. Judge that behaviour, sure. But there's no call to write them off entirely.