What should I do about this?

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The girl I have been speaking to for just over a year now is speaking to another guy. There was nothing wrong with that since we weren't official. However we both like each other and it's about that time to take the relationship to the next step and make it official. The problem is when I first started speaking to her she had said in a comment on Facebook that she would that guy. A year on and she still talks to him sometimes but tells everyone he's a friend. I see him flirting with her on the social networking site and she never rejects him or directly accepts. She always uses words like maybe and mm.., never really saying she will or wont do something.

I wouldn't be comfortable with those two communicating if I got into a serious relationship with her. I mean who would be comfortable with some other person wanting to bone their partner and trying to flirt with them all the time? I don't want to tell her not to talk to her friends anymore but I don't like the situation and don't consider their relationship to be a friendship.
A year ago she told that guy she would date him.