At my college, you could make arrangements to rent an entire "room"--in reality, a multi-bedroom apartment--from housing directly. You could then have whoever you wanted living in it, presumably unto not having anyone but yourself, if you could afford it. This included co-ed rooming situations.
Actually, I had a roommate who kind of moved her boyfriend in with us. It's one of the reasons we got housing to make her move out.
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Gillian
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"