Help! He's cut off contact

This is my first post here.  A brief summary of my situation:   For over 3 years I have been in a long distance committed relationship.  Our relationship has been tough for the past 2 years because of the distance, the fact that he was out of work for 18 months, which meant all visits were done by me, and the fact that he has a sleep disorder (long sleep syndrome) which means he often sleeps for very long periods of time (12-15 hours is not uncommon)...even during my once a month weekend visit.  Anyway, after trying every which way to express my unhappiness and feelings of not being appreciated and acknowledged, I came to the point a couple months ago where I could envision leaving, though I don't want to.  I then started putting 2 and 2 together and began studying adult ADHD and so many things became clear to me.  (He admits he has it, but then retracts that statement when confronted, and has never been diagnosed or treated...I feel VERY strongly that his untreated ADHD is destroying our relationship, but I won't go into loads of detail right now).

  Anyway, I went to visit on Thanksgiving (our first time seeing each other in 7 weeks because, once again, he couldn't come here because things kept coming up with work).  We ended up getting into a huge fight (seemingly out of nowhere) on Friday night.  We are both very hurt and angry...he feels I am always blaming him for things and always too negative, and I feel unappreciated, unacknowledged and sick of feeling lonely even when I visit.  He was very upset that night and eventually I wound up leaving and driving 5 hours home in the middle of the night. 

I haven't heard from him since.  I know he likes his space when he is upset, but I am stuck in limbo and don't know what to do.  As hurt and angry as I have been, I do not want to end this relationship.  But he is super defensive and refusing to accept the possibility of the ADHD (and everyone else thinks I am just a pushover who needs to leave). 

My question is...How do I approach him now?  I know that I cannot control anyone but myself.  I know I cannot save a relationship alone.  I am trying to give him space and not keep hounding him, but I wish I knew the magic thing to say that won't make him feel like such a failure and so angry.  I don't want to make things worse...but it is tough because he is at the stage where he thinks I am making up all the relationship problems and that if I just "let things go" we would be ok.