Nightshade - I don't want to start sounding like a broken record on the boards, but I recognize so much of my H's behaviors in your H - and in my H's case, clinical depression was the problem. Somehow a little prozac in him made most of my flaws disappear! I really noticed the last time his depression reappeared how short and irrationally irritable he became with the kids- and this from a guy who is usually superdad! Once he restarted his prozac he went back to being his usual good-dad self.
I know it can be hard to get a guy to admit he needs treatment for this. You might try bringing the topic up gently - but it has to be in a very non-threatening way. Or maybe you can sneak up on him - get him to start taking B vitamins and fish oil capsules for his heart, buy a light box "for yourself" but let him get some exposure to it every day, get him out exercising on a regular basis. I know it's hard when you're really close and the gun is aimed at you, but recognize this is his illness speaking and try to help him. It will pay off.