Help with trust issues?

After being in a relationship where I was cheated on, and in another where I was suddenly and unexpectedly abandoned, I've developed major trust issues. Fast forward two years of being single, I found a new relationship with a girl who is unlike anyone I've ever met. I can tell her absolutely anything, and she listens and understands. Only thing, is she has a crap ton of guy friends, hangs out with them one on one on a regular basis, and is close with her ex. I've told her I hate all of that, but that I don't expect her to stop because it's not my place to tell her who she can and can't hang out with. And she tells me that she wants to help me get over my jealousy and that I shouldn't do it alone. But to be completely honest I can't. Its so hard to trust her. The other day she turned me down to hang out because she was busy with homework and I respected that. Next thing I know she's texting me telling me shes hanging out with some guy. The fact that she told me tells me she had nothing to hide, but when I pointed out what she did to me she was really sorry and afraid and took responsibility for what she did. Apparently she cried because she was so afraid of me being hurt and dumping her and her friend she was with said they shouldn't hang out anymore because of how upset she became. Its these things that show me she isn't doing anything behind my back. She's just oblivious. I'm forcing myself to trust her, and give her freedom, but its clashing with my insecurities.