So my point in all of this (sorry it's so long) is: How do I go about forgiving MYSELF for the role I willingly played in all this?
Simple. Just forgive yourself.
I know, I know. It doesn't
feel like it's that simple given your headspace right now. But the truth of the matter is neither you or I were born with manuals on how to deal with someone else's addiction, or how to counter codependent behaviors. And as a result, we made mistakes.
The mistakes you made weren't from a place of malice, but rather a place of caring for a sick person. And in your best thinking at the time, you did what you thought was right in supporting him. Hopefully as you grow, you become honest enough to recognize where you went off the rails, and then you learn not to do what you did again.
Speaking for myself, I am grateful for the experience I had with my AXGF, as painful as it was. Why? Because I grew as a person. I recognized how f'ed up some of my own behavior was, and was so successful in not repeating it, my AXGF left me because I didn't enable her to be helpless anymore. And I recognized just how fortunate I was to have the gifts I have and the people in my life. It's so, so easy to ruminate over what you think you've lost, and it's so, so easy to not pay attention to what you do have.
The goal is not to beat yourself up. The goal is to identify where you went wrong, learn from it, and then not repeat the same mistake. In AA, I believe this is referred to "another f**king opportunity for growth."
So, knock it off.
With Affection,
ZoSo