Girlfriend is really distant

Past few weeks my girlfriend is seeming distant to me, we've been together 6 months now and she looks upset at time but when i ask her how she is she replies with im fine. We have been together for six months now. But the problem has been happening the past dew weeks. For example a couple of weeks ago we talked about a guy in our school who is her friend but i said i dont trust him as hes butted into relationships before. She got annoyed at me saying i didnt trust her and that she has it under control but he just continues to flirt with her and she doesnt even noticw it. Since thwn ahe has been acting distant and strange. Even when we kiss she seems eager to pull away than before. I dont see her cheating. She really isnt the type of girl to do that, she wont even do anything sexual with anyone so i dont think cheating is an option here, at least i hope not. If you can just look over and reply aboit the situation it would be very appreciated.

This other guy has already butted into your relationship because it's causing problems for you by your gf's reaction to your concern. When you look at her actions and then listen to her words, things aren't stacking up. Your gut is telling you something's wrong. Sit her down and ask her for a direct answer because if she was committed to you, she wouldn't put herself in the situation with this other guy. If he respected her properly, he would respect her relationship with you. You also need to consider, that maybe she could be gradually drawing away from you regardless if this guy is in the picture.