Wow, I identified strongly with your experience.. My AH had stopped drinking (although not for 26 years--mine lasted 5). I recognize all those symptoms you talk about leading up to the relapse--the depression, the wistfulness and talk about missing drinking, the unhappiness with the marriage.
His relapse occurred almost simultaneously with our youngest going off to college. He had been more or less the stay-at-home dad while I worked and travelled for business. I think his responsibilities had helped to hold him together--once that glue was gone, he was undone.
When he relapsed, he drank, he went to singles support groups (even though we were never separated during that time--I think he was trying to backfill what he probably expected to be the end of one relationship with a new one). He cried, he complained about me. He went to a "guru" whom he completely manipulated in order to get the permission he was seeking: This woman who I'm sure was well-intentioned but very ill-equipped to counsel an alcoholic, told him, "You're wife is controlling you--why SHOULDN'T you have a glass of wine with your steak?" So that's just what he did.
Meanwhile, I was thrown for a loop; I was in a tizzy--but like you, I went back to AlAnon and also got a therapist.
I just wanted to assure you that I understand everything you said, because I experienced the same thing. Thanks for your story.