In Maryland you don't have any rules about renting rooms.
Just kidding,
Maryland defaults to a state lease even if money has not changed hands. Seems like you are being kind to your roommate, so follow up everything in writing.
In the event of something going wrong, you want to fall back on having given notice for him to move on January XX etc etc.
The fact that the roommate doesn't pay everything or on time just means the roommate is short on money. Keep in mind that this is very short term in the big picture. So don't get mad for the sole reason that you live with this person also.
Maryland rental laws are somewhat interesting. In many places if you rent to two or less individuals you do not have to be a licensed rental. The license often comes from the city or the county.
Go up the page and look for Landlord/tenant laws. There look for Baltimore Neighborhoods...this organization advises people all across Maryland.
--108.18.xxx.xxx