...but the simple fact of, "What if?"...
What if...situations are just as likely (if not more so) with "straight" roommates. What if...you have a non-out gay roommate that comes out in the middle of the year and looks to you for support because he's not getting any from his parents? What if...your drunken wannabe frat boy roomie decides that your laundry is the perfect puke basket? What if...your drunken roommate decides to try and use your poop chute as a bottle opener when you're sound asleep? What if your roommate decides that while studying the week of finals, leaving the room is unnecessary, even for bathing and relieving themselves? What if...the possibilities are endless.
...While it's true that the OP might want to embrace the situation, it's entirely OK for him to feel uncomfortable about it. That doesn't make him homophobic. Not yet, at least. So stop accusing him as such.
[Edit] I suppose that personally, there's a difference between 'uncomfortable' and 'homophobic.' Homophobic seems a bit extreme to me.
Technically, any "fear" of gays is a form of homophobia. That said, a little uncomfortableness at this situation, given that he's a freshman and going to a new school and all, is probably normal.
I'm going to recommend, as strongly as possible, that you don't switch, and it has nothing to do with your future roommate's lifestyle...if you change after being assigned, they'll pair you randomly.
This is true. No one I knew that changed roommates after being assigned a roommate liked their new roommate any better. Some were a the same level of discomfort, for others it got worse. It's odd that they didn't ask the usual things (late/early person, clean/messy, quiet/loud in addition to the smoker question).
Also..another thing i'd like to mention, I am an only child, the only space i've ever had to share in my entire life has been with my parents.
Well...this could spell trouble, especially if your new roomie (whether you decide to change or not) is in the same situation. Here's some advice, start leaving your door open all the time from this point forward. Sleep with your door open, shower with the door open (close the door for toilet stuffs). Just get used to being around and seeing people at times that you aren't used to, because that's the biggest adjustment you're going to have to make, no matter who your roomie is. Also, start looking at your stuff, decide what you think is a decent amount to take. Then spend then next couple of days trying to figure out how to live with only half of that stuff. Taking too much stuff is the biggest mistake I've seen people make and it's the easiest way to piss of your roommate.
I still hope you decide to chat/talk to this guy and at least give him a shot. If it is mainly about you feeling uncomfortable in situations where his friends are visiting (I dunno how far the two of your live from the uni you are going to), then talk it out set some mutual ground rules. This is something you should do with any roommate anyway (for example, overnight guests only when the other roomie is visiting their parents, or one night a week prearranged in advance, or hang a sock on the door, etc).