Marle,
Your really getting hit between a bf and drugs. I am so sorry she is choosing to go back with him. It sounds like she thinks you will let her have her cake and eat it too. I hope you tell her she can't have it her way.
I know that will be hard Marle but she either cares enough about you and her recovery with you in your home or she chooses to throw it away.
Feelings are tough enough to deal with on a plain basis but him doing drugs is just a killer for her.
Stick to your boundrys, no maybe's, no just one day, no nothing just as it has been. Look out for you on this one because you have done great and if she chooses to stay with you and away from him wonderful, if she doesn't you can't change her thoughts. Then you need to look out for you no matter how selfish that may seem to you..it isn't. Your special too! Stay strong! And were here:ghug