That's a sad story (about the guy finding your letter) but I had a similar experience.
My ex-wife left me for a coworker and I was a bit resentful. She wound up with the guy and we sold the house and we had no kids but he had a wife and two young children. After drinking at her, I came back to AA and started an inventory. At work I'd get these rageful thoughts and would jot them down on a sticky to later transfer to the 1st column of my inventory. Some of these stickys fell out of my pocket and someone at my work found them and she had the same name as my ex. I heard she freaked out a bit. Someone explained to her about my ex but she still thought I was some kind of freak. She'd be right about that one fo sho.
So I'm sober now and married happily. I do inventory yearly and I tell my wife that if she should ever get a hold of my inventory, she will probably see her name come up. If she ever gets snoopy and decides to read it, then that's her problem, because she just became responsible for it. In the end, the first 3 columns are just ego talk and a lie anyway. Our 1st column and 2nd column are the truth as we then see it, but it's not about the person, place, or principle we're writing about. It's about our life and our own ego at that moment.
We don't hold anything back in our inventory. It is for this reason that I now only write in a spiral notebook and I keep it by my side and am very careful to never leave it laying around. It's mine. It's personal. It's none of anybody but one other person's (person you 5th step with) business. Oh, and God. And I only 5th step with another recovered alky who will be helpful and not effected by it.