Legal Question in Real Estate Law in Maryland

Re: roomate disputes

You didn't indicated in your question who are the signees on the lease and thus legally in possession of the premises. I'm assuming from the tenor of your question that it's you and the other fellow, but not his girlfriend. If so, you have a right to approve all significant changes in the living situation, including whether or not the girlfriend is allowed to be there in the first place. After all, even though she sleeps in your roommate's bedroom, presumably she uses the common areas of the apartment, which in effect diminishes your use of it.

The dog further diminishes your use and enjoyment of the common areas and you can rightfully object to its presence. At the least, your roommate should be shouldering 2/3 of the rent if he's not already. In that case, your rights wouldn't be as strong, since he's already paying for the girlfriend's presence--although not necessarily the dog's.