odsjnsakdmdslk What an interestingly little predicament.
I couldn't really know what to do, either. While getting it out right away to make sure there isn't a problem is all fine and dandy as well as efficient, but the first thing out of your mouth to him shouldn't be:
"So, hi!"
"Hi. Looks like we'll be sharing a room!"
"I AM HOMOSEX PLZ DUN HATE."
You should probably get a bit cozier and friendlier before dropping the subject. Or, you could just test the waters WITHOUT telling him upfront. Find some way to weasel it into conversation, see how he reacts. Judging by his reaction, you can probably take it from there as far as switching rooms.