It doesn't sound to me like you're talking about a solitary mistake; from what I understand, it sounds like someone was taking advantage of you and never really had your best interest in mind. If I was put in that position, I would have a difficult time finding reasons to stay. I know it can be tough to leave someone because of the experiences you've shared together, but people tend to change and not always in the way you want them to. Just because they were doesn't mean they are or will continue to be. You can't expect to make anyone happy if you're not happy yourself. When it comes to relationships, you HAVE to be selfish, and if you find someone you love spending your days with, you'll find that being selfish means doing whatever it takes to make each other happy.

Anyways, I'm sorry if that seems placating; that really isn't my intention. That's really what's worked for me in my experience. I love my wife. I love my son. It makes me so happy to make them happy. I guess the gist of what I'm trying to say is that it's not worth it to compromise. Just do what you need to do to be happy, and when you are, the people around you who truly care about you will be, too.