It depends on the situation. No one should ever cheat and they never have a good enough excuse to do such a thing. If that were to happen to me I could stay with that person because I couldn't ever trust them again- what's a relationship without trust.
I will leave .. because once a trust has been broken you can never bring back the same feeling you have for him or her .. you'll always have a doubt and this will just lead to arguments. Though it's possible not to leave if your love is that really strong.. but for this scenario it just means that the guy or girl is not contented for the love he or she have thus makes cheating.
Everybody deserves a second a chance, however it will always depend of the gravity behind his cheat. What I mean is If the reason is acceptable and it is not that heavy to accept, then forgive. Once is Enough. Trust is very important.
Ill break up with him and I wont trust him again!! even if he have an excuse well thats not enough to make me forgive him or forget it !!! cuz if he did that once he can make it again! thats what I think.
Good question and I love the wording! It depends on the circumstances. If the other half felt neglected and wasn't receiving enough attention from you, then I would understand. I often think that people cheat as a result of a void they feel between them and the one they should me monogamous towards.