Do I have a legal recourse if my room mate left 4 months earlier than the lease was due?

If the roommate signed the lease, or had an agreement with you to pay part of the rent through the end of the lease, you would have a breach of contract claim against the roommate. You could enforce it in small claims court.

Yes, against your former roommate, but the landlord, generally, can collect all of the rent from you (or your ex roommate

You can take your ex roommate to small claims court to recover any damages, but you need to pay rent an attempt to find a new roommate.

If your roommate signed the lease as well, your landlord may have recourse against both of you if you break the lease. If your roommate leaves you behind, you may also have recourse against your roommate. There are many possibilities here. If your roommate leaves, and you cannot pay the rent, you could be subject to an eviction action for non-payment of rent. If you are able to pay the rent, you should try to continue to do so to avoid an eviction on your record. You could then pursue your roommate's half. If you do get evicted, you could still pursue your roommate's share, but you will have to deal with the eviction on your record which will make getting another place very difficult. You might consider discussing the situation with your landlord to see if there is something that could be worked out to break the lease early or try to find a replacement roommate. If your roommate wants to leave, they should probably consider finding a replacement as well to avoid leaving you in a poor position. It would be a good idea to talk to an attorney about your specific situation to see if there are other, more preferable, options available for you to pursue so that you can avoid any negative consequences as possible.

First, examine what your lease says about subletting, and take steps to bring another roommate in. Ask your landlord to get a writ of possession as to your ex-roommate. This will prevent him from claiming he has a right to return to the property. The above is important because when you are harmed, you have a duty to mitigate (reduce your losses). Second, you can sue your roommate for the amount he owes you. If it is under $5000, you will be in small claims, which is generally friendlier to self-represented people. Your local clerk of court should have forms and/or information about how to file a lawsuit.

Typically, joint tenants are each liable to the landlord for the full amount of the rent. Between themselves, in the absence of a contrary agreement, they are liable for one-half each. So, if you pay the landlord more than one-half, your roommate owes you. He probably is not liable for whatever other damage you may suffer by being evicted or finding other housing.

Was your roommate also on the lease? If not, then you may owe the rent but if you had an agreement, hopefully in writing, with your roommate to pay rent then you may have a breach of contract claim.

As to your landlord, no. You will need to speak to him/her and see what you can work out. You can sue your roommate, but the likelihood of collecting anything and in a reasonable time is very low.

Not really unless you can arrange something with the landlord.