As a former landlord, let me give you the landlord's point of view:
"I don't care what your problem is as long as I get my rent from either or both of you. You leave, he pays. He doesn't pay, I sue both of you, get judgments and collect from whoever's got the money."
Your roommate will have to pay the full rent or be evicted. He will have good cause to sue you for indemnification - and win.
None.
No.

