C.S.
He needs to talk to someone and probably needs to be on medication-at least temporarily.
It's the tough love route, but if he won't do it voluntarily, maybe you need to say that if he doesn't it's a deal breaker (of sorts). He doesn't owe it to just himself, but the rest of you are suffereing too and it's a selfish act to refuse to get try to get better. He's married/a father-it's not all about him anymore.
Remind him he's not a failure and that the only 'failing' would be to not deal with the depression that is affecting everyone.