Having suffered from depression myself, I can categorically say there is nothing you can do to make him happy. He is not capable of being happy at the moment.
For me, once I recognised and accepted the depression, medication was essential. It took at least a year of trial and adapting before it had a measurable, lasting effect.
During this time I got up, went to work, parented, did housework, participated in family life as usual. Basically I put on an act but nothing made me happy. My husband describes it as 'The year you went missing' as, despite doing all the things I usually did, having the conversations I usually had, he said he'd look at me and behind my eyes there was just a vacant space.
It was a horrible way to live for both of us but neither he nor I could not have changed it without help. Eventually I found a medication that worked and I slowly got better.
I am grateful that we got through but, if I had not got medical help, I would not have been surprised if he left .... in fact I'm not sure I would have noticed and I love him dearly.
Depression is a terrible illness. If your partner won't help themself you need to help yourself, you can't heal them.