Roommate allowed another to move in w/o my or landlord approval

[cgelliott]

I lived in Apartment A with my roommate Will from March 23, 2007 until about a week ago. I moved into Apartment B with a Co-Worker of mine across town. I am still on the lease until March 23, 2008 at Apartment A. I let Will know that I intended to pay my half of the rent at Apartment A as well as Apartment B until my lease was up at Apartment A. The other day, I swung by Apartment A to pick up any mail I had and to grab a few things that I still had stored in my bedroom. Come to find, there was a cat that greeted me at the door. I thought this was odd since Will had never had any pets. I didn't think much of it until I walked into my room and found someone else's bed and belongings filling up my room. All of my remaining items had been put up in a closet. Will had allowed someone else to move in! I was completely unaware that this was going to happen. Unfortunately for me, I am still on that lease which means I am legally obligated to pay half of the rent until March. My landlord told me I still had to pay and that he would handle the situation from here on. But now I'm curious. Will knew that I was legally obligated to pay half rent. Was he telling this new occupant to pay half, too? That way he didn't have to pay rent at all? Or was he and this new occupant both only paying a quarter of the rent a piece while sticking me with half although I vacated a week ago. Not to mention that I could be held responsible for whatever damages the cat could cause to the apartment. Is there a legal term for abusing the fact that one is legally obligated in that way? If I were to get a lawyer involved, what would we be going after Will with? Please respond. Thank you.