He sounds exhausted and depressed,,lacking motivation to get moving ,and to cope with his own 'pipework!'
I wonder if some antidepressants might help - have you chatted with the Dr about it? Its difficult to get the head /mind away from focussing on bad health times - have you had a holiday recently? Is he getting out into open spaces, to see nature/ have a walk (even if its only a few metres at first) ? As the spirit lifts, so appetite picks up . It takes a long time and a lot of energy.
I hop things get better for you both.