Why isn't my husband ever happy?

We have been married for almost 6 years. Since I've known him, he's always been unhappy at his jobs. And he's had pretty good jobs. A couple years after we got together we started our own business, which I ran full time for a couple years, but it wasn't bringing in enough money, so I got a full time job. Then he hated his job so we agreed that he could quit and try to get the business off the ground again. It's been about 9 months and we are doing ok money-wise, but definitely not as well as when we were both employed full time. I'm comfortable, but he stresses about money all the time. He doesn't like working for other people, he doesn't like working for himself because he thinks it's stressful. (didn't think it was stressful when I was doing it). So WTF is his problem? Why can't he just deal with work like everyone else does? Yeah, my job sucks sometimes. My boss pisses me off, but it's not the end of the world. It's just a stupid job. I don't let it negatively affect the rest of my life. But he does, and it drives me crazy. Nothing makes him happy. We have a beautiful home in a good neighborhood. A great balanced social life. Supportive families. We're very comfortable. But he's "just sick of it". He's "sick of everything". Trust me, I have talked to him about all of this numerous times. Then it gets better for a little while, then he's right back to being pissed off at the world. It's so annoying.
Added (1). Sometimes I think he just wants to go back to being a bachelor, with no pets and no kids, no mortgage, no responsibilities. Just his things and his space. What a baby.

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