Yes I can understand how there are a variety of factors that come into play, that contribute to you feeling anxious and at times, mistrustful. It's important that you realize you two do have a good and honest relationship. One that was based on true friendship so the foundation is established.
I think that what might be needed here is to have a talk with your girlfriend that of course you want her to hang around friends, but maybe there could be some kind of agreement or understanding that certain people make you uncomfortable. For example, maybe she could not hang out often with those she had a crush on or those who are friends with her ex. See what she says about that...maybe she would be willing to do that, and see your point. It's reasonable to bring that up. Now that she is in a relationship with you, it's about the two of you deciding what is mutually acceptable for both of you. So, use that open honesty that you have with her to talk about these things. Also let her know that you trust her, but would simply feel much more comfortable if she saw friends where there was no romantic interest or connection. That seems reasonable and of course let her know you would do the same for her.
Again, trust her, unless evidence shows otherwise in the present time. And also speak up with what is bothering you and the two of you reach mutually agreeable solutions.