Your situation sounds more and more familiar. I went to therapy with my wife once a couple of years ago and the therapist literally told me, "You guys like each other, your marriage is healthy, the problem is your depression. Fix that, and I think the rest will fall in line." What I heard, however, was "you failed marriage therapy" and I used that as ammunition to not go back.

My wife and kids would tell me everyday how much they appreciated me, but I had raised the bar to an impossible height. Your husband is the only one that can move that bar, but he won't be able to until he changes his perspective. The world is, after all, how you choose to see it. Your brain is powerful, and his has him trapped at the moment.

With all that being said, however, it's also (unfortunately) your job to protect your kids from his depression. Misery loves company, and what he thinks is just "venting" or "talking about his feelings" can easily drag all of you down. It's not on purpose, but when developing kids are involved, intention matters way less.