My girlfriend is not normal. I understand woman have friends. But how far do woman draw the line on friendship?

MY girlfriend and I started dating 3months ago. We both go to the same school. She has a dude in her cl who she says is her Friend. So ok cool. We have problems like regular couples do. She turns to him and, tells him about our problems. He tells her about his problems to. so ok they both are in a relationship, but coming to each other about their problems. Now get this though, Im a man. I know how men think. So weeks past and all that. When i dont have time to take her out to eat or movies, she goes with him. They exchange phone numbers and all that. One day when he saw me in the hall way(I didn't know) he told her he can her better then me (ually). So she tex me i better her good tonite because another man wants to.? What girlfriend will tell her boyfriend that? Anyways we did have and I did put it down. but I guss it was not enough because she still cheated. she said he just ate her out 2x. after she told me to lay it down good. So im like what the hell. She said that they were just friends.So im like if he told you he wanted you after he saw me that day. That is when he cross the line of friendship and told you his plans basically. He wanted to be more then just friends the whole time. Get this. She said after he said he can do her better, she still went to the movies him and out to eat but as "friends". Woman when help me out. she dont talk to him no more and al that but still. Who is rite me or her. I said he wasn't a friend no more after he told you that. I told her that' when she shouldve cut him off as a contact. I still think they went beyond just oral. she Said she didn't kiss him or nothing. Just just hung and he ate her out 2x. I think they had in his car. She said when they came home from the movies one night they just sat in his car and was talking, one thing led to another and boom. so help me. Am I rite for this old thing or wrong? What is a male friend to woman? this guy or something else. Did she wanted this guy? Is that why she didn't tell him to fall back after he said that? O last thing. She had a picture of him on her facebook. She never had mind on there. I had to tell HER to. But with him she did. Her excuse was she was trying to get hook him up with another woman. lol I told her hes a grown man with kids. I really dont think he needs help finding a woman. especially if he got her Without another woman's help. She said every woman is different etc. Ok i understand but still. Why is it so hard for me to believe her. maybe because I dont know any woman or dude to just do oral, and movies out to eat,. woman mature woman please help me on this one. Thank you.