that's the point of hanging out in a group isn't it? your post seems a little selfish. you want the gf to hangout w/ you and your friends but not to create friendships of her own lol.
i became friends with my exs friends gfs and despite the fact we broke up, we still talk to each other. for the most part, when we were dating, we did talk about the boys but it wasn't anything like purposely badmouthing them. just girl talk.
your gf's life does not revolve around you (at least it shouldn't) so you shouldn't assume that she just talks about you the whole time she's with them.
relax man, you're making a situation out of nothing. it's GOOD that gf is friends with your buddies girlfriends.
look at it this way, your gf couldve been jealous that buddies gf hang out with you too... coulda bought a gun and shot em all up
then shit would get really real for ya.