If Allison's BF can't stand his roomies, too bad. That's (usually) what you get when you live in student housing (if that's what he's in), unless you choose your own roommates, and even the best of friends can turn out to be complete toads when it comes to the roomie situation (been there, done that, got a large single room the following year all to myself). Well, maybe not toads, because I don't want to give toads a bad name...but you know what I mean.
Getting back to my original point: if Allison's BF doesn't like his roomies, boohoo, too bad, so sad. Allison may be a nice girl, but it sounds like she's also a pushover when it comes to the sex-type thing (not unusual when you're young - been there, done that, learned to be assertive). She needs to be more assertive and more conscious of the inconvenience she is causing you and your other roommate (who, like it or not, are paying to live there, while he is paying to live SOMEWHERE ELSE).
The harder solution would be to get them to spend more intimate time in HIS apartment, where, whether he likes his roommates or not, they might have a more appreciative audience for the free live sex show.
No one should have to put up with a potential bladder infection just because they can't get to the bathroom for fear of disturbing the two lovebirds. No one should have to rearrange their study time, computer time, sleep time (or sleep location!), which they are paying for. You need to sit Allison down and have a very frank talk with her about having consideration for everyone who lives there, and that means spending a few nights down at the BF's, whether he likes his roomies or not (personally, I think this is a big fat excuse to put the girls out rather than the boys - which group is more likely to take action to put a stop to this?). If they absolutely, positively cannot do this, then they need to make arrangements to get a more private space to have their amorous liaisons.
While I lived with roommates, unless I had my own space in which to "entertain," I didn't do so out of consideration for my roommate. My good luck was that I was mostly attracted to upperclassmen or students who lived off-campus so I had excuses to be off-campus to be "entertained" during those 2 years. The 2 years I had my own space, all bets were off. Allison doesn't have your room to herself, she has to share it. I'm not saying she should turn into a nun while she lives there, but either cut down on the "private time" that keeps you from your space, your sleep time and your study time, or make arrangements so that you know when she's in need of some "private time" - the old scarf/tie on the door, a "Do Not Disturb" sign, or something like that, but the main point is that it should not interfere with your use or your enjoyment of the facilities you're still paying for.
If you live in some states (like CA), the general rule of thumb for figuring out the maximum number of people who can occupy an apartment (not sure if this applies to on-campus housing, but this is for private apartments) is 2 people per bedroom plus one - so in a 1-bedroom, that's 3 people. In private apartments, having an extra "long-term" guest like that would be enough to be considered breaking the lease, and could get you kicked out. Might not be an issue here, just saying.
There's no reason why you should have to avoid these two, if they're choosing to have "private time" in a space that is anything but private. If they're adult enough to pursue "private" activities, they're adult enough for you to point out that it's not cool for them to pursue those activities when other people need your shared space. Sure, it sucks to be in that situation, but you all have to share that space whether he likes it or not. He's paying to live somewhere else. There's no need for all of you to be sympathetic and accommodating to his distaste for his roommates. If he doesn't like it there, he can move elsewhere, not make your living situation an intractable one.