Problems with girlfriend hanging out with another guy?

Ok so it started when she accidently forgot to log off her Facebook and when I happen to get on the other day I was curious and looked at her inbox messages. When I was looking through them I found out that she was flirting with another guy behind my back (we where 4 months into our relationship) what bothered me is that when the guy asked her who would she f*** she said her ex boyfriend, but anyways this guy goes to the same school as I am and like they seem close and stuff so it bothered me... I told my girlfriend that it bothers me that she talks to him and is physical with him than other guy friends. she told me that she liked him but I don't know if it was as a friend or not. so like one day she told me she was going to stay after school for a art club thing to see if it was fun but she seemed to be in a rush plus she said she was going alone(which I thought was un-usual for her to do) when I was heading out I bumped into that guy and asked him what he's doing and he said he was staying after for this art club thing so I figured they set it up without telling me... I don't know what to do so my heart became really hurt. I told my girlfriend why she didn't tell me she said that she had no knowledge of him showing up (I think she lied) so we where arguing about it and stuff later on in the conversations she said that she was going to hangout with him... do you think its right to do such a thing then say she's going to hangout with him? what should I do about this guy? I don't like him around her and I tell her that I don't like it but she acts like a doll that says everything I say which I don't like...so I was like whatever do what you want...so she still continues to talk to him he texts him more often then she does with me (form the looks of it) ...do you think she might cheat? so far she claims she loves me and that she won't ever do that...i don't know what to do...please help?
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+1 y
oh and like when she says she's staying after she acts like she's in a rush and stuff...but when I stay after I always wait and escort her to her bus before I go to a club...
Problems with girlfriend hanging out with another guy?
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