Well, I don’t think this is something you should sweep under the rug. It’s completely unacceptable. This is a clear infraction (better than “interrupts me”, even though that might be more corrosive to the relationship in the long term) and you can use that as a line in the sand. Get help (have a specific thing that you want him to do – counseling or drs appointment, etc) or this relationship is forever changed. And here are the consequences if you choose not to change. (I don’t know what the consequences are for you – that’s personal – but once you have it clear in your mind, you can present them to him and then he can see what the actual danger is.)
ADHD doesn’t mean unreliable as in disappear for 3 days… it means it can be harder to be on time for things, or something might slip your mind. For me personally, it’s a huge struggle to remember to get to the bus stop in time to pick up the kids. Now they’re old enough to come home by themselves, but for 4 years, I never EVER missed it. Worst case, I wasn’t quite at the stop by the time the bus came, but they could see me. This daily consistency was made difficult by ADHD. But it was important to me, so I did it. Your husband is on a whole different level.