Hiding, retreating by the ADHD member?

I'm trying to find out if this is a trait of my husband's personality, or a feature of ADHD, so I wanted to know if anyone else ahs experienced this from their spouse?

When my husband gets stressed, or upset, or anxious, he is irritable and snippy whenever he's around us, which isn't much, because he runs away. He hides from whatever is bothering him. He won't talk to me about it, just loses himself in his game. If the stress is job-related, he will burn through all of his vacation time to run away from it, or spend large parts of his day out in the smoking area with his iPhone to avoid it. At home, he'll retreat to the bathroom while the kids are awake, and after they're asleep he'll get on his computer and put his headphones on, and just won't talk about anything. He's defensive, angry, snippy, and just generally unpleasant to be around.

I want to help him, to be a sounding board or someone that can help him find solutions; that's what you do with someone you care about, right? But he just won't let me in. He's done this for the 7 years we've been together. We lived together for a year prior to getting married, and it was one of the most miserable years of my life. I was depressed over our living situation (long story, but basically forced on us by our jobs), and he was too. He retreated into his games, leaving me out in the cold, which furthered my depression; his ignoring me, and being "unable" to help me, furthered his depression and forced him deeper into his games, further from me. Finally I gave him an ultimatum, which I normally don't, but it had to be done: either come up for air and talk to me, include me in your life, or I have to move on. It wasn't an idle threat; despite the pain it would cause me, I was willing to follow through with it.

But I can't do that anymore, and I don't want to keep issuing ultimatums; I want to figure out how to help him understand that I'm here for him, I'm not attacking him, and his retreating from the world drives a wedge between us; with a child with ADHD and another child going through the "terrible twos", with no support nearby, he and I have to be a team; we're all we have. Any suggestions? Thanks!