Its not you...
I am a recovering alcoholic and addict, and beleive me, it wasent the drugs or alcohol that was the problem, it was always my THINKING!!! I have been clean and sober for a few 24 hours now, and I still think like a drunk and addict from time to time. But aa has given me the tools to use so I dont act on those thoughts. Him treating you like he does is not your fault its his, thats how we drunks and addicts act. Unless he starts using some tools, he will never change.
PS Once a cheat, always a cheat!!!
Please take care, and god bless both of you