i was the bipolar roommate many years back.. i was not well medicated at the time & looking back i was a nightmare to live with... i'm very fortunate that my ex-roommate is still my friend... though we did go for a few years without contact after she moved out... and i don't blame her one bit..
if you're planning on moving in with someone, definitely ask yourself all those questions suggested by drskipper... that's a great starting point... also consider how well managed your illness is right now & whether or not it's a good idea to add so many variables into the mix by moving in with someone... also, be prepared to tell whoever you're considering moving in with that you have these issues and how they affect you & could possibly affect them at some point... don't sugar coat it.. better to let them know ahead of time, than move in and face a living disaster because they had no idea what they were getting into..
whatever you do, i would advise against moving in with a friend... it's the one of the best ways to ruin a good friendship... never understood why people always said that until after i had a few roommates and almost lost a best friend...
i have determined, i can't do the roommate thing again.. might save me money, but it's not worth the cost to my sanity level...
best luck to you!