In this post you state that you have no verbal contract--then you write that your roommate told you what and when to pay, you agreed to it, and took the room--guess what your agreement and acceptance of the room made that a valid oral contract! You do have a contract!
Best option is to negotiate with the roommates--find a person to replace you--they will not go after you if you take steps to keep the cash flowing--in the end, that's all roommates really want. Best of luck
READ THIS BEFORE CALLING OR EMAILING ME: I am licensed to practice before the state and federal courts in Virginia. Addressing your issue does not create an attorney-client relationship and I AM NOT providing you legal advice. You should speak with an attorney to whom you have provided all the facts, before you take steps that may impact your legal rights. I am not obligated to answer subsequent emails or phone calls unless you have hired me. I wish you the best of luck with your situation.