I'm so sorry for your pain. My son is an oxy addict and I too am going thru the same hell that your experiancing with your BF. I've done thru the disbelief, the optimistic hope that he will realize what he's doing and stop. The denial, the rage and sadness you feel everytime they lie, manipulate and steal from you to protect that mistress (addiction). The reluctance to let go of the hope that they will turn their life around and recover but it doesn't happen and the hopelessness that follows. Then finally, the realization that this is what they are, addicts. Even when they are in on-going recovery.
While I applaude your effort to stay with him while he's actively seeking recovery let me caution you. Addicts are masters at deception, and they guard that mistress carefully. Be very careful about letting your feelings for him blind you to whether or not he is lieing. I have to remind myself daily what my son is and capable of but I will always love him.
I have withdrawn all support save putting a roof over my son's head and that too is about to disappear which takes me to a whole different level of dispair because I was raised that you don't turn your back on family but I'm choosing to fight to not be an enabler anymore. I've heard of many more people that haven't recovered from addiction than those that have. No one knows better than those of us that have walked in these shoes how hard it is to let go of your addict. I can validate every experiance and feeling that your going thru. All I can say is this, educate yourself all about addiction so when the time comes you can make a decision based on knowledge. In the end only YOU can decide when you've had enough and walk away with no regrets.