Cheating

Curiosity has seemed to get to me yet again..... It seems like everyone knows at least one relationship torn apart by a cheating spouse, but why is that!? Why can almost no relationship hide from this tragic occurrence? I have been cheated on numerous times but can proudly say, even with the pain and revenge I wanted after finding out,  I never cheated on any of my partners. I just want to know for those who do/ have cheated, what lead you to it? For those of you who were cheated on, what was the excuse you were given for why it happened? And in either case, did you stay together?