The only silver lining I can see there is that he most probably knows his resentment is totally unjustified and unfair. That won't make him feel better of course, but he'll know.

Doing some physical work in the house is a good way to work through a depression (for him, I mean). It doesn't cure it, but it does give you something to at least feel a bit good about later on. "At least I did XYZ.". He would also feel less guilty. It would ease tensions. He should try it. Not just me saying that, it's a part of CBT - not a miracle cure, but I found it to be helpful, both when I'm down, or when I'm in pain.