She broke the agreement, not you, so make the separation legal if you can't accept it 100%, and return to each other. You didn't say how she wants it to go from here with the other guy.
My wife and I agreed to seperate for 6 months. Part of the agreement was not to see other people.Today she tells me she is pregnant and it's most likely his: another man's child. We had sex 1 time and they had sex 3 times within 2 weeks! What should I do?
Well, how much do you love her?
If you are willing to look past the fact that she lied that is one thing. What about if the child turns out to be the other man's? Then what? Are you going to bring him up as your own son and just forget the past?
Hey pal, sorry to hear about this and I don't want to influence you as this is your life and only you can make the calls here, but I can tell you that personally if my wife did the same to me there is no way in hell I would take her back. Or at least if I did, she would have to work very hard to prove her trustworthiness ever again.
Damn that's rough. Poor guy. I wouldn't like to be in that situation.