All roomates are bad roomates, IMO, it just takes time for them to turn bad.
Being a roomate is a process of compromise and it seems like the ability of your roomate to compromise has expired. I understand your point about wanting to avoid the childishness of him trying to interrupt the game. I can foresee an pre-argument to the effect of "We're gaming anyways, so you just have to deal with it." This would be followed by him turning on the TV at 5PM, really loudly, and starting a fight. I'd suggest you avoid this if you think it's at all possible. In fact, if you really do think it's at all possible, I suggest you plan on moving out or getting a new roomate or something. People change, and this guy has changed for the worse. It's not likely to get better. Chances are that he really doesn't like to relinquish the living room and has been dealing with it in the past, he mentioned it to one of his drinking buddies (never good people, btw), and got pressured by his drinking buddies "not to put up with it." Am I right?
Anyway, your GF issue has a lot of impact. Don't underestimate the awkwardness of it. Your roomate undoubtedly feels very weird about it and probably doesn't appreciate it in the slightest - regardless of whether she pays rent or not. If notifying her parents is a bad thing, avoid the chance -- remote as it may be -- that your roomate will call them, "Hey, guess what Oryan77 is doing..."
So, the final advice is to find somewhere else to play. I'm 100% sure that this is the best option has the repercussions on pushing your roomate are not worth the risk. Options for gaming:
Friend's place - You seem to have exercised all these options. But, maybe a new player ...?
Library - Never tried it myself. If not the school library, how about the public library?
Hotel - This is, quite honestly, brilliant. It's not cheap -- I mean, it would be $45 you wouldn't otherwise spend -- but there are a lot of benefits. Maybe the whole group can take a break to swim in the pool. Etc.
Paying the roomate - Although seemingly brilliant, I don't like it. It still carries all the risks from above unless you get something in writing -- and that would look bad.
Restaurant - Perhaps a restaurant, coffee shop, or something? I'm not sure what choices you might have available in that regard. As long as you keep ordering, they might not have a problem, but Saturdays are probably busy.
Work - Can you use a conference room at work perhaps? I knew some people who did this. It was particularly nice because of the free work-beverages and overhead LCD projectors and networked computers (a little fragging break never hurts).
FLGS - Our FLGS would allow it, for a small fee of around $10 I think. Dunno for sure, since it's been soooo long since I checked.
Bookstore - Some bookstores like Barnes and Noble have big tables. That might work. Might not.
Outside - On a nice day, you could always do it outside in the park or something.