My husband has expressed concern several times in the past that he was the cause of my depression.
I have tried my best to reassure him that he was never the cause. I have told him that there may have been things that he could have done to help, but I know he didn't do because of lack of knowledge. And it's pointless to wish that he was wise enough to help me when I couldn't help myself. It was never his responsibility...always mine. I knew something was wrong, I knew I shouldn't feel the way I was feeling and I had no idea how to fix it.
But if my husband had demanded that I go to a doctor and get checked out, I think I would have dug my heels in. It wasn't until I was in the hospital that I was finally desperate enough to try the anti-depressents.
Looking back on it, very stupid of me, considering how much they really did help me.
Please don't blame yourself. The best you can do when someone you love is depressed is ease their suffering a tiny bit. But it's going to take a real professional to really help him. And that is no reflection on you in any way. I'm speaking from personal experience so I hope I don't offend you. I may also be projecting a bit here as I wish I could convince my husband of the things I've said to you in this post!
In any case, please do something to help you feel better.