To me your story comes across as if you're asking if you did the right thing, more then asking if you're the asshole. In your context I think you did what you felt was the right thing, and there's no way to objectively deduce if you did. But hearing your tremendous loss, I can hardly imagine not doing what you did.

Considering the purpose of AA, and how you obtained your information, I think it wasn't right. It's not the AA's or it's members/attendees role to find out or determine if anybody addiction is dangerous to others. Other parties, organisations, the employer, etc, are responsible for the general checking of performance.

This is why ultimately I say YTA. But, you can be the asshole and still have done right. I am so sorry for your losses and I hope you'll be able to find a way to cope, and also hope this will help find you just that little bit of closure.