Irrational?

So lately I've been feeling insecure in my relationship. I think it's because we might have to do LDR in September and that really puts me on edge. We were hanging out at his friend's cabin this weekend and though I've met his friends I've never met their girlfriends. One girl was very nice and we really hit it off but then later she kept getting very close to my boyfriend. They played beer pong on a team together and she kept 'falling' into him. He was friendly with her and nothing happened but I just felt very unsure and insecure. I thought about talking to my boyfriend about it but I know he'll say there's nothing going on and I know there isn't (he really has no time to cheat). But I feel so insecure and like I'm losing him (a little bit). Does anyone know how to deal with this?