What to say and do to encourage a depressed, chronically exhausted, chronically bitter and angry husband?
This is not accusatory, but merely a suggestion.
I think that self-reflection and introspection are the first thing to be done. Use empathy. Put yourself in his shoes and ask yourself to what degree you are responsible for his depression, exhaustion, bitterness, and anger.
Sure, there are plenty of things around us that can prompt depression, exhaustion, bitterness, and anger. Many of those things are completely out of his control and your control, but you do have control of anything that you do.
So, first thing, reflect and fix any and every contribution of yours to your husband's state.