I'm only supporting what others have said here, FF. Bancroft came to write the book as a result of his work as an anger-management facilitator for abusive men. That work taught him the men were not helpless victims of their own anger. When you read it, you'll learn what he learned. He doesn't prescribe any particular course of action.
In "The Verbally Abusive Relationship", Patricia Evans says that she's seen some men resolve their issues and stop being abusive - indeed, her Freedom Programme offers courses for abusive men. Bear in mind, though, that she says a very small proportion of men really do want to change and do the work required (in context, she says she's never seen a female abuser change.)
Your partner's drug abuse is probably an effect of his deep-seated issues from childhood - not a cause of his anger, just another symptom of it. As Atilla told you, the only way through this and out the other side is via serious therapy, and plenty of it. It would take years - more than five, up to twenty - of regular, committed psychotherapy. And he'll probably get worse before he starts getting better, IF he sticks with it.
Read the Bancroft book. Don't share it. Use it as a source of expert information on a syndrome, then see what you think.
Well done for getting this far. Good luck!