I'm so sorry for your loss of Lenny. That big sweet face, of course you miss him. I want to reiterate what AlaskaKat referenced to above. Lenny went through a lot in regards to his health but you clearly went to lengths only someone who truly loved someone would go to, to bring him back from the edge several times. Towards the end, he may not have been physically ill, but his mind was not the same. You mention you had to increasingly make efforts to keep him calm and to avoid his triggers, which seem to have added up over the years and become more frequent and more aggressive. I know it hurts, and no time at all could ever alleviate the loss, but consider his quality of life towards the end. He clearly was not in control of his triggers or his anxiety or aggression. I think of the experiences of owners here who've lost pets due to dementia and the like, and what it must have been like for their pups to suddenly lose time, forget where they were, not be in control of their feelings and fears, it would be torture for a human who could have their condition explained to them, but for our pets, its more difficult. Lenny would never knowingly hurt you or your husband, this is very clear from what you've expressed about him when he's in full control of himself. Your safety and well-being was just as important, and you had a responsibility to yourself and your spouse, and family, friends, strangers on the street, and especially Lenny, to do what was best. How horrible would it have been if Lenny himself got hurt during one of his episodes? If you or your spouse were hurt so severely that the choice was taken away from you?
I know none of this makes it better or fair or easier, and I know it doesn't bring Lenny back, but you gave him many good years, and love and patience that most would not have afforded. You made a decision that helped ease his suffering mind, and prevented a situation in which Lenny could have hurt you enough that he would feel the pain of hurting his beloved. I know that Lenny thanks you for setting him free, now he can run and play without fear or anxiety at the rainbow bridge. Please do not continue hurting yourself over this. What you did was an act of love.
Again, I am so very sorry.