Re: Husband and Son hate each other
One thing I caught that I don't see anyone else touching on, but I'd like to, is your son's ADHD. Both of my sons have ADHD as well. It is a daily struggle to deal with a child that suffers from it. The lack of attention, the hyperactivity, it's all very stressful. While it doesn't excuse his behavior, I wonder if your husband does what he does because he simply doesn't know how to deal with your son. My boyfriend, when we got together, knew the "on paper" ADHD...but had never dealt with a child that had it (they are my sons, not his, although I refer to them as ours since he acts as their father and their bio dad does not). I had to kind of teach him how to interact with the boys. It wasn't this "ok, now do this" kind of thing, but more of a situation where when his reaction to something they did seemed overblown or somehow inappropriate, I'd sit down with him and explain to him how best to try to deal with them in that situation. It was a process, took a while for him to learn, but he did. Now, of course, he's always had a good relationship with our boys, anyway, so I think that may have made it easier. And that means that the very rocky relationship your husband has with your boy will make this more difficult, but I think trying to teach him better ways to interact with your son could help.
I also agree that some counseling is in order. Their relationship seems to be so bad that I think, even if the ADHD is contributing, they'll need a lot more help to repair the relationship. They'll need professional help.
Talk to your son too. His resistance to dad probably doesn't help either. And while it's understandable that he would be resistant, they both need to find new ways to deal with each other. If one changes and the other doesn't, the same situation will continue to occur.