Ya know.. if all of this is due to all the stress, of your DH.... then THAT has to be solved.
Or your son will continue to have, problems. Emotionally.
Just because DH is removed from the home, does not mean that the "problems" are gone. BECAUSE, the emotions of a child... is CUMULATIVE. From the past, too.
Perhaps, your son, would benefit from Counseling or Child Therapy.
Your son's home life, was not good. As you said, your DH was VIOLENT and abusive. These problems, does not just go away. They accumulate, within the child. A child does NOT have "coping-skills" or the ability to deal with it. Thus, they get emotion based problems.
I think your son needs some sort of Therapy to help him. Deal with it all.
What he has gone through, with DH like that... all these years... is very, toxic for child. Its repercussions, are lasting and harmful, psychologically and emotionally.
A young child, simply CANNOT, cope and manage with all those problems, on their own. And for all those years.