The question raised by the OP brought to mind the 12 step programs I had read about and am glad to see them posted here. In later years I felt guilty about not offering more help and support to someone I divorced years ago due to his addictions. I tried to implement the above steps but found the process was not as simple as it looks. I discovered my ex had re-married and I felt any contact from me would be a harmful intrusion into his marriage, so I didn't contact or follow up on him. I was recently saddened to learn he had died alone from his addictions having no longer been married for several years. So I hope forgiveness comes from spiritual means.
I think we all have stories we gather during our lives, if we are decent human beings who care...and who grow. I have to remind myself that Step 9 says "...except when to do so would injure them or others." You sure couldn't do anything while the guy was married. It's tough to know when to draw the line between being accountable for the behaviour of others, and I don't believe there is one universal right answer.
(from Quora) Did the children who were brought up in Hitler Youth continue to believe in Nazism after the war because they had been indoctrinated when they were young? The son of Hitler’s private secretary, Martin Adolf Bormann, was one of ten Nazi children, heavily indoctrinated pretty much since birth. He recalled the moment the radio announced that Hitler had committed suicide in Berlin, and that “all was now lost”. Young Bormann was in the Hitler Jugend at the time, a teenager, surrounded by other teenagers, each of them indoctrinated to a ridiculous degree. Several of the boys looked at each other. Intensely. Sadly. Then walked out of the door of their barracks, onto the field, and shot themselves through the temple or the roof of their mouths. To kill oneself was consider the highest honor, following their ‘great leader’, a bit of a German bushido warrior thing. Soldiers and officers, even young kids, killed themselves by the thousands out of loyalty to Hitler and the Third Reich… Martin junior and his best friend looked at each other. Considered, for a brief moment, to kill themselves as well, as their friends had just done. Then they shook their heads, threw their guns, and walked out of the building together. They decided to live. Bormann decided not only to live, that day, but to unlearn his indoctrination, step by step. He eventually became a Catholic priest and a fervent anti-fascist. So did many other people who grew up during Nazi-Germany — older Germans born during the 1930s and 1940s are among the most fiercely anti-Nazi people you can find, anywhere. You may have read about the madness; they lived through it.