Unfortunately, I think he has you between a rock and a hard place. It would be different if he wasn't paying half the rent, but b/c he is on the lease and is still paying, then it does make a difference.
On the other hand, you can always speak w/ your landlord, explain the sitch w/o giving too many details, see if he/she will change the locks and/or let you out of the lease.
Im still standin better than I ever did looking like a true survivor feeling like a little kid Im still standin after all this time and Im picking up the pieces of my life without you on my mind..
