Since you mention depression, have you talked to your doctor about putting him on an antidepressant? This could be the answer to his problem. Many seniors DO become depressed as they get older, as they begin to think about their own mortality.
I've had to be on an antidepressant most of my life cause I have clinical depression, but I remember that my Dad started to become depressed as he got older. He withdrew, he wasn't quite 'himself' and even tho he always was a bit cranky, he became even more so.

I could always get around his crankiness cause I knew how to handle him

-- my sisters were scared of him, but I just bowled right over him, and he never knew how to handle me. LOL He actually enjoyed it. But an antidepressant helped him and it might help your husband too.
Talk to your doctor about it. Perhaps it would help -- it's really worth a try, don't you think? I really feel for him, because after dealing with depression ALL my life, I know how miserable he must be.
I wish you and your husband all the best. Please take care and God bless you both. Hugs, Lee