The bounced checks are a serious Red Flag. They were later covered, correct? If not, then you should have filed a case against him.
Bad roommates are a nightmare; the problem is that you are both on the lease and as such as "jointly and severally" responsible for that lease, in other words, you are both legally responsible for the lease even if the other is negligent. A conscientious rent-paying tenant can be evicted due to a deadbeat roommate.
You have the option to file a court case against him. You can talk to the landlord about getting a new roommate after the negligent one is forced out by the court- that is, if you have a good case. As long as rent is paid up, he may be difficult to evict.
Alternatively you can try to find a replacement and get out of there. But this needs to be done with consent of all parties.
You can request that he leave; he might agree. But you've got to cover rent, either out-of-pocket or through a new roommate. There are rare occasions when a landlord is understanding and might give you a break if you can't cover rent for one month because of the bad roommate- but I emphasize this is rare (I have know landlords with college students do this, because issues among roommates are common).
PS: This is my 10,000th answer. The reason I started Yahoo Answers 10 years ago is a bad roommate! I was looking for advice online and came here.
2d PS: It is false to state that only a landlord can evict someone. A tenant, or a group of tenants, in a shared rental can file a case in court against a negligent roommate and have them evicted.