I had a girlfriend a while back that was still "friends" with her ex. Then he started coming around at random times on the weekends seeing if I was there or not. He tried to be friends with me. I wouldn't have it. I knew what he was up to.
Then a while later I found an email saved to my computer archives from him asking my girlfriend to come back to him, because he'd made a mistake. (Yeah I'll say, he beat the crap out of her.) And all the replies after that, which were also saved, were saying "I had a great time last night" type of stuff. I looked at the dates, and they were when she was supposed to be shopping with her mom.
I confronted her about it, and she said she hadn't done anything, and she would never take him back. But one month later, after coming home for lunch to surprise her with roses and Olive Guarden, I find her riding him like a mechanical bull on my couch in my living room.
Needless to say I kicked them both out at that point and I neglected to give them back their cloths before they were "escourted" out of my appartment.
Moral of the story? Your girl will choose whoever she wants, and if she doesn't have the guts to stand up to her ex, you're the one that will get the brunt of the pain. She will try and have both. She will cheat on you, and she won't want to choose. And if you're lucky, by your actions, and by you stepping away and saying "Hey good luck with that, call me if you need help", She just might say "Damn it, now I have to make a choice", and you just might be that choise.
Good luck to you... if this is, in fact... the situation. What was that other thread about that I saw? I'm corn-fused.