Sounds like he is giving you the run around. A little bit of a lame excuse to blame the amount of time remaining in this semester! I would be worried about his vague excuses, lack of emotional commitment and generally not being completely open/honest.

Why is he concerned about being friends with your flat mate - maybe because if you two did get it together and things went "wrong" the atmosphere in your house could become pretty bad.

From your post (and your other one about trying to achieve an orgasm) I get the impression that your pretty innocent.

I think you already know the answer, if you have sex with him and his still non-commited to you...you're going to feel gutted! It's a risk, but then again...if you're not bothered and just after sex then...whatever really...