Um, how old are you guys? Crushes (for that is likely what this is) can happen at any age, though they are more likely when you're young.
And by roommate, do you mean you live in the same apartment or are you, literally, sharing a room? If you are sharing a room, and you can afford it, I suggest that you find a way to change the living arrangement. If the guy is straight and you make a move on him, you are likely to kill off the friendship, and I suspect you don't want to do that.