Welcome sorry that you are having to deal with this situation, however, he is just doing what addicts do.
I woud suggest that y6our read all the stickies at the top of this forum and the Family & Friends of Substance Abusers, lots of great information at your fingertips.
His disease is a progressive one, without a strong recovery program it will get worse. And, since he is copping your meds, I'd say he is also addicted to pills;
Read around all the Family & Friends forums, it will help.