Can you get him to move out? Whose name is on the lease/mortgage statement?
If not, just stop paying his bills and either stay with your relatives or go get your own place.
You can tell yourself--and him, if you want--that you're giving it 6 months. If he's still off his head in six months, then fine, you've given it a shot. If he pulls himself round and is doing better, then maybe there'll be a chance for reunion.