I can see potentially serious and long term downsides to any decision you make, and I don't know nearly enough about your situation to advise. He's always going to be your childrens father no matter what, and a dozen years of marriage plus the relationship before that is hard to just dismiss. On the other hand, a shattered trust is very hard to repair. If all parties aren't deeply committed to it it's impossible, and still requires a lot of time and effort. If it ever happens again I expect the damage is always irreversible.

There's probably nothing in that you didn't know though. I'm so very sorry; THIS is why you don't cheat, people, not because of the consequences to YOU, but because of what it does to the person who loves you when they find out (and they ALWAYS find out, sparky. ) Sigh. You and your family will be in my thoughts and prayers, and I wish you well, whatever you decide you have to do.