not real sure why it was only 1/2 of the rent as you were 1/2 of the tenants but anyway, small claims court is about your only recourse if he will not pay you willingly. Getting a judgment still doesn't mean he will pay you but it can give you some options.
Oh, and the LL can come after you if you were not removed from the lease you might want to check the eviction as they would have to evict both parties, not just the one.

