Sunny brings up a good point. An affair the symptom, not the problem. The fact that someone would have an affair is only indicative that the relationship was ALREADY in very rough waters. The reason many couples break up after an affair is because it is undeniable proof that everything is not 'OK'. Until then, its very possible that both could lie to themselves and say, 'We're just both busy and stressed with work...' and not deal with it.
My parents stayed together until I was 19. When they separated, I encouraged it. They were absolutely miserable! Night after night they had fight after fight and I could hear them all.
Don't stay together for 'the kids' or any other reason than for YOU. Kids are happy if their parents are happy. When the parents are miserable and angry...