I sublet my apartment to this guy. The guy refuses to pay the last month's rent. He signed a sublease agreement. Do I have a leg to stand on?

Of course you have a leg to stand on, but your case is against your sub-tenant, not the landlord.  Your obligations to your landlord under your lease are unchanged as a result of your subleasing.  If your subtenant has failed to pay the last month's rent, such that you had to pay it yourself, you can sue your subtenant in small claims court for the amount owed.  Of course, this will be easiest if you have a written sublease with him, but even without one, you have an oral contract that can be enforced in court. This answer is given in accordance with the laws of Virginia and may not be applicable in any other state.  It should not be construed as legal advice, as that would require a more thorough analysis of all of the facts involved in a specific case.  If you need further information or assistance, please feel free to contact my office for a consultation. Case results depend upon a variety of factors unique to each case. Case results do not guarantee or predict a similar result in any future case.