My girl went back to her ex, what to do?

My girlfriend I been seein for about 4 months now has been talkin with this ex I don't like. Its normal for her to be friends with exes, but I myself have a "no friends with exes" rule. I knew they always talked and knew they were still attracted. When I started seeing her, we started as friends and it moved swiftly into relationship, due to attraction and common interests. I didn't know she was seeing this other guy and how serious they were, whether they were on the verge of demise or whatever, but this dude emails me and says they been dating for a while before me and her started seeing each other. I asked her and she said that it was over between them because they had no interests or connection really, just physical attraction and he was "a nice guy" but whatever. He then went on to hate me for "stealing her away" when I didn't even know they were dating, if they still were or not. Now recently she deletes me from her facebook, lists him as her boyfriend and says she "doesn't know what she wants to do" and is "really confused" and I hit the roof, I knew deep inside that she still liked him and vice versa. I spent a day collecting my thoughts and last night she contacts me through AIM. She said she was bored and needed something to do. Normally we talk or play video games online together. I felt this was not my place anymore. I told her to talk to her man, but she said he wasn't around and she "had no man" weird. She went on to explain she only listed him as this to get rid of someone from her past that hates her and is out to get her, and I find this really childish if its true. But anyways, I told her she got her man back and I am happy for them and she gets mad at me. If its true, I know they are doomed because he works a full time job and goes to college full time, he has no time for her and she is very needy. I love this girl but I dont wanna rush back into this and make mistakes. Any tips on how to win the girl back and make this dude look like a chump?