faith,
I feel for you and the situation you are in. I do not have any experience in this area - I did not learn that my AS had a problem with oxys until after he had moved in with his gf and I had moved in with my daughter. We have not lived together in the past 3 years. His father & I divorced about 10-12 years ago, I have not been in a relationship since then and my AS has very little contact w/his father.
I imagine it is stressful having that hanging over your home every day. I hope any one with step parent issues will be along to help you out with suggestions. I just wanted to let you know I am thinking of you.