How to deal with her love of guy friends!?

My girlfriend seems to have a thing with having guy friends and this has been bothering me like crazy. When we first met, all she did was talk about her guy friends etc and I told her I did not like it and she stopped talking about them. Now, she is the type who says that she grew up around a lot of guys and that she was treated badly by a lot of girls when she was in high school. She says she has always found it easier to make friends with guys and be among guys because they do not judge her etc. Now, I have told her that this bothers me and that I do not appreciate her hanging with guys all the time. She even still hangs out with a guy she was seeing about a year ago, although it is a group setting, but the fact that she is okay hanging around an ex even when she has a boyfriend is troubling for me. She still keeps in touch with all her exes and her best male friend is an ex as well. They have known each other since she was 16 (22 now). We always fight about this issue and I tell her that it all makes me uncomfortable but she is adamant that I do not trust her and I am insecure. I just do not know how to handle this because she seems to want to keep her guy friends but usually girls slow down on guy friends when they have a boyfriend. I just have a feeling that something is not right here. Now, I saw on her phone that she added a guy by the name of James on her bbm and he was saying he wanted to get together with my girlfriend’s group of friends. They also added each other on facebook. When I asked her about it she said she only went to see a room in his apartment for rent. Is she hiding something? What should I do about the whole guy friends thing?