Worries from afar

Ok this is the first time I've used something like this but here goes... My girlfriend and I had been dating for 9 months we are very close. Practically married she stayed over at my apartment for almost 3 months straight without going back to her townhouse. Then she had to go to grad school out of state. About a 7 hour drive away. It hadn't even been one month yet and she keeps bringing up this guy named Mike who she works with at the office of her grad program. Then one time she mentioned that he wanted to see a movie with her and she wanted to know my thoughts. I told her I wasn't too keen on the idea. Then I felt bad later and told her that I trusted her to use her good judgement. One day after telling her I trusted her... she ended up going to a movie alone with this guy. A girl was supposed to come along with them but she couldn't come and my girlfriend ended up going anyway. I was furious because we had just discussed how much I didn't like the idea of her seeing a movie with him. So we talked about it a ton and it blew over. Now she's back at it again. She brought him up yesterday out of the blue in a conversation on the phone. She had her little sister bring up four dvds from her home in my state just so this guy could borrow them. I told her I thought that was weird that he's borrowing movies from her little sister. So we had a mini-argument about his name being brought up since it was still a sore subject with me since the two of them went out on their movie together. Then just today she mentions to me "Do you mind if I go see a movie with Jazmine (her other work friend), and Mike?" In that moment I wanted to say no... but she was going to be with another girl so I guess it might be ok. So I said yes. I've been going crazy all day though thinking about it though. Stressing over it. When I talked to her after the movie was over and done with tonight. We talked for 45 minutes and she never brought up the movie. I didn't mention anything because I wanted her to bring it up. So anyway here is my problem. What do I do really. We are separated long distance there's nothing I can do to keep this guy away from her. I don't want to be the controlling boyfriend though and tell her what she can do with her free time. I just hate the whole thing. Does anybody have any advice? Should I just tell her how much it hurts my feelings that she spends time with other guys while I'm sitting alone in my apartment here waiting for her calls? I'd appreciate anything you guys can tell me. Thanks!