Why do people who have been cheated on?

why do they forgive the betrayal? Can they really put it on the past, can they really say they are happy? why do they put the kids as an excuse? or is it that they are just afraid of being alone. i just can't imagine the humiliation, the pain, this causes. i'm grateful that "for now" i haven't had to go through this, hoping never will. but if for better or worst this happens i wouldn't be able to take the image of him and another woman. i just couldn't i'll be living a lie. i know we are humans and those who cheat are not so bright, but why do they put themselves in that position, and affair doesn't happen in one second. so why can't they walk away, what do they need to prove? and why want to stay with the wives (sometimes). i'm not trying to put no one down is so not my intention. but can't we love our selves more, and expect more, deserve more, as humans. and this is so true to husbands who have been cheated on too. there is no excuse either for a man or woman. if not happy leave, be honest, at least give that much to the spouse don't you think? what i'm trying to say is that i'll rather know before hand (the affair) then later. at least he won't be with me more , so it won't be any of by business who sleeps with no matter how much it hurts.