There's an issue running through the whole thing that refusal of the person with it to deal with ADHD creates terrific pain and trouble for family I'm glad, for your health, that you are where you are now.
“What should I write in my letter to my husband to make him stay?”
Let him know how he still makes your heart flutter when he walks into the room or how you love that he puts your toothpaste on your toothbrush for you each and every morning.