Is my jealousy get in the way of my happiness or will it show I care?

I love my girlfriend and I've been with her for 5 months. We are perfect for each other. Problem is all her close friends are guys. They are always being sexual with her even when I'm around. She laughs it off but still it pisses me off. Sometimes we fight over it but I end up letting it go and apologizing but it clearly bugs me every time she gets texts from them or we go out with them. They don't really talk to me either. I know guys and most guys aren't friends with girls to be just friends. That's why I have an issue. I try and make her see my point that I care and worry but she says I don't trust her. It's them I don't trust but how can I get that point across?

Updates
I just checked her phone. Might seem psycho to many, but it read (from one of the guys I don't like) "if he's around, try to get away so we can talk about tomorrow ;)"

I don't know anything about plans for tomorrow. Should I still try to be trusting and see if she says something?