I would be inclined to think that guys who have friends who are girls, at the same time as having a girlfriend, usually know them before the girlfriend comes on the scene. And it seems a bit odd, to be honest.
So my gut feeling would be that something's going on. Even if nothing has actually happened, are you going to feel comfortable with him hanging around with another lass while you're away - I personally couldn't deal with that. lot's of drunken phone arguments I expect. Not really what you want to be doing at university - it's meant to be fun!!
I suspect your bf misses having a girlfriend around. But if he lied to you about seeing this other lass, it's probably because he's got something to hide. Either way, if you're going to have a long distance relationship, honesty is paramount. And he doesn't seem comfortable with that.
Good luck honey!!!