I'm sure worrying about how your semester is going to turn out isn't helping the stress. And massive amounts of stress JUST from school alone probably has a lot to do with the depression. What classes are you taking?

If you have to get away from your roommate for a while take one of your textbooks and go to the library. I spent a LOT of time at the library the one year I had an awful roommate. It doesn't even mean you have to study the whole time, maybe just browse the random books and sit and read something random for a while. Relaxing in that way would certainly help your stress a little bit.