I also have a DP who suffers from depression sometimes it is more series than others but it is always there. I completely get what you say about not being able to voice your own needs.
Here's what works for us.
My DH recognises that he has a mental health problem - he takes this medication, goes to therapy (and does the homework). We're never 'over' the depression, but I know that he is trying. For me, this is important.
From my side, I know that when he is in a bad state he needs lots of sleep, a calm, tidy home environment, and nourishing food.
I also plan activities at the weekend that take me and DS out of the house - library, swimming, and trips to the park. We could then have shorter periods of family time when DH could plaster on a smile and interact (dinner, film etc.,).
I had to give up my idea of how I thought things should be, and adjust life to the reality of what it was (is). This sounds a bit depressing but it can be liberating and can make dealing with his depression less tiring because you're not fighting against it (if that makes sense).
Finally, finding time for yourself is very difficult but can you find time during the day - lunchtime, going to/from the office to build in some meditation, read a book, meet up with a friend? And/or you can see a point in the near future when that might be possible?
How old are your children? We were able to shield DS from the worst of it when he was a toddler, now we can find age-appropriate ways of signalling when DH needs to rest/more space.
So hang in there, you are not alone there are plenty of us who know what it's like.