Your summary of the questions sounds very much as if the simple understandings attached to those letters ADHD that are primarily associated with school age children and learning disablities does not clarify anything.
It is extremely complicated symptomatically and despite the advertising it is not food related.
I have had the luxury of having had a son with it and then finding out after retirement that I also am a raging Adhder. Priviledged because of hours and hours of time to read and research this. After all that there is no one book or website I can send you to.
What i can say is that everything I knew i have thrown out and perhaps your husband does as well. Just a few years ago it was not considered an adult disease.
Secondly most of the medications are designed to improve focus and concentration. We can focus but only on the interesting (to us) activities that fire up our brain.
This doesnt necessarily improve our notoriously inconsistent working memory eg Pick up the kids at daycare, carry out the garbage when You next go out. The losing the keys gisease its often called. It doesnt explain the nasty reaction to certain materials in clothing and our shear exasperation at labels on shirts that aggravate us no end. It doesnt explain the dark side of RSD Rejection Sensitive Dysphoria where we believe that all criticism is personal rejection and we fly into a rage. As a child this shows up as a temper tantrum. It doesnt explain why we fail to filter a response, verbal or action before thinking it through because our brain is not equipped to.
It doesnt explain that when it comes to social clues we are clueless. We will not pick up,on hintseasily. That we seldom start something complicated and actually finish it. That because something is complicated we may put off starting it for an eternity. That we keep talking long after everyone else has heard the Quiet order and ceased. This is a particularly risky action when police or others are involved such as customs agents. Of course this does explain our extremely high rAte of incarceration but not our very high rate of addictive behaviors.
There is another reaction to RSD that cripples marriages and that is when we turn inward and shut down because of our anger and disappointment with ourselves and give up trying and communicating. Perhaps why, as undiagnosed adults we are most often treated for Depression first which leads to a later or concurrent ADHD Diaqgnosis.
All of these results trace back to the inability of parts of our brain to develop normally because the neurotransmitters Norepinephrine, Serotonin, and Dopamine are in short supply aNd messages are not getting through as well or as often as they do in a normaal brain. In many of us different parts of our brain are activated to work on problems than are used by normals.And the usual parts atrophy or grow far less robust. Pre frontal Cortex to name one.
This is not a complete list of unusual behaviors but is a good start. Treatment options exist for all of these but if afflicted with all of these and you still havent left him perhaps the place to start is for both of you to seek education on it. There are a number of excellent authors but you might just start with the list from “Totally ADD” That is by no means complete.