I recently moved out of an apartment with a roommate. We paid 1400 dollars for a security deposit (700 each). When we were planning to move out when our lease expired, I submitted my 30 days notice in accordance to when our lease was to be up. The landlord accepted my 30 days notice separate from my roommate however my roommate never gave her 30 day notice and moved out when I did. He now is keeping 900 dollars of our security deposit from my roommates failure to give a 30 day notice. How do I get my portion of the security deposit back? Do I have to go after her? Or can I request it from him? My question is, Legally If he accepted my 30 day notice separate from my roommate but is keeping a joint deposit, what was the point of giving 30 days in the first place?

The point of YOU giving notice is now you have grounds to file in Small Claims Court against your roommate. You complied with the terms of the lease. He/she did not.

When you sign a joint lease you are BOTH responsible for the entire rent and security deposit. There is no half and half arrangement with the landlord.

Your half and half agreement was with your roommate.

Go to Small Claims Court and file.