I think the anger/shame/blame/deflect/refuse may be inevitable. He’s also feeling the affects of your guys marriage, and his ADHD has almost certainly strained other relationships. One of the nasty things about ADHD – we can sense it, but we’re not equipped to figure it out.
Suggesting getting tested is a good idea because of the genetic component. If you can get the information in front of him, there’s some chance he’ll have the same “AHA” moment. It may be ugly. But it’s his ADHD – he can’t do something if he doesn’t know, and you can’t do it for him!
All my love!