I completely understand the impulse to research, to try to find answers, to put things in categories that might actually make sense. The problem with this situation is that it’s a pretty classic chicken/egg situation...what came first? The addiction or the personality disorder? And which personality disorder? You can end up in an endless mental spiral trying to understand what can’t be understood.
I do think that addiction mimics many of the symptoms of several types of mental illness...and the more deeply addiction sinks in, the more those similar attributes appear.
If you truly think it helps you to try to research all of this, that’s one thing...but if you know in your heart that what you’re really trying to do is come up with the magical “answer” as to how he ended up like this and how you didn’t see it coming, maybe try to let it go. Some things just happen to us without explanation and many of those things suck.
Be as gentle with yourself as you can, yes?