Marriage in trouble

My husband of 11 yrs was recently diagnosed with "severe ADD".  He got the diagnosis after our son was diagnosed.  The diagnosis came in the midst of martial problems...I found out months earlier that my husband was having an affair with a so called good friend of mine(to my knowledge it is still ongoing).  Knowing he has ADD explains alot of his behaviors, but does not excuse them.  I have been very willing to work on our marriage, but after a year he still has not admitted that the affair was wrong. He has refused to move out. He shows no remorse nor regret.  He still blames me for the affair and all of his anxiety. He also blames his parents for many things. I have read several books on ADD and each day I am learning more. He is seeing a psychiatrist. I am seeing a psychologist and we are seeing a therapist together. We have made no progress as a couple because he cannot decide if he wants to be married or if he wants to be single? He is in on concerta and ritalin, still working on the dosing. As the year has progressed, I have seen more destructive behaviors occurring.  He made a comment that the "void" will never be filled.  My question is can a person with severe ADD really change their behaviors? Why do they blame others? Am I kidding myself to think he could change  and that he could ever understand the impact of his actions?