The black sheep are the ones you can save the rest of us. You are doing that.
My family was not dysfunctional or alcoholic. (I married into one that was. So I've seen the devastation which alcohol wreaks.) But even though I was spared your situation to a degree, I can still have compassion for what you went through.
My heart feels for you without words. My head says that you are punishing yourself unnecessarily for what was a loving act on your part. I suspect your mother carried that same memory to her death. The way out is for you to get that you were both innocent in a crazy, crazy moment. We just have to give each other those moments.