My roommate... we get along fine, but he comes back to the room wreaking like weed a couple of times a week, which can get us both written up and fined.

(I'm okay with smoking weed, but only in safe situations or parties)

Also, we have completely different sleeping schedules.  I stay up late (2ish) doing homework and get up right before class; he goes to bed at 11 and wakes up at 6:30 to do homework.  He's also a huge hick, and annoys me on a daily basis (mainly lack of respect for my shit).

I'm not sure on what grounds they paired us up on.

He's leaving this coming weekend to go home for a couple of days.  When he's heading out the door, I'm going to tell him that I won't be here when he comes back.  But how do I put it?

We haven't even had an argument or fight.  I can't help but expect that he'll be completely thrown off guard.  Through his eyes, he has no reason to suspect that I want to move out.

And I want to preserve what friendship we have, and get this over with without pissing him off and hurting his feelings too badly.

So how do I broach the subject, and what do I say?