I'm going to agree with LemonBlossom and suggest you talk to the LGBT contact at MIT. There may even be some kind of register for roommates that they keep that are LGBT and LGBT-friendly, you never know.
That aside, since you want the roommate experience, I'd go with it and go out. Just be out when you get to MIT, no holds barred...you're in a whole new place, why not just be the you that you want to be seen as?
I know you're worried you may not find a roommate that jives with who you are, but I don't think that should be a deterrent. Why? Because that's a risk for ANY roommate situation. Some people don't like how long you take in the bathroom, some people will hate the scent of the food you cook, some people will hate you for your religion, your skin color, your interests, how loud you need the television/radio to be, your night life, whether you enjoy sex or hate it, whether you enjoy drinking or hate it, whether you approve of drug use, whether you approve of skipping classes, whether you're a mega studier or mega partier, whether you approve of having people over, whether you approve of having the opposite sex over...the list is endless. I even moved into an apartment with a friend of mine who apparently didn't feel the need to disclose that he has mega social anxiety issues and some hoarding tendencies. This meant that I wasn't allowed to have parties, he flipped his shit whenever my partner came over (no, he wasn't in love with me...he did the same thing when I took him out with a female friend of mine), and he cluttered the place with loads of junk mail...even expired junk mail containing coupons he'd never use (example: he kept expired coupons for dog washing discounts even though we didn't have any pets). This was a friend of mine...one I had for a while and hung out with, and when I was homeless he even let me stay on his couch when he lived with his mother and sister in a cramped apartment. I've been out with this guy having drinks, we've gone places with a mutual friend, so the fact that he had social anxiety never, ever crossed my mind. It seriously sucked in some aspects when I was living there for a year...but at the same time, we still had shit in common (we are friends, after all) so we focused a lot on that.
Even if your roommate doesn't approve of who you are, you'll almost certainly still have things in common. At least you can both go to the store together for food shopping or help each other with homework as needed. You know, basic human stuff that two people living together would do. Maybe your roommate won't approve of who you are, but maybe you have the same taste in movies so at least you two can high five while watching awesome flicks.
Finally, having to live with someone who doesn't approve of something so central to your being teaches you to be more tolerant of other people, may teach that person to be tolerant and that there's absolutely nothing wrong with people like us, and also teaches you how to be more diplomatic and deal with different people, especially people who don't agree with you just because you're you. These are all wonderful silver linings to pull out of any storm cloud.
I'll respond to anything but am partial to chief.
"Life hands everyone shit. It's what you choose to do with that shit that determines if you're happy."
"Complacency is a shitty reason to be miserable."