Well, I have a different opinion. I agree with you, DU - this sounds like clinical depression (compounded by MLC/turning 50/career insecurity).
What might you do to help with this?
First - can you suggest that he get his thyroid and testosterone levels checked? Low levels of either of these hormones can cause weight gain and depression.
Second - does he snore or have sleep apnea? Untreated sleep disorders also cause weight gain and fatigue.
Third - can you do anything to make the finances more stable or discuss plans with him for career change/ early retirement? Part of the MLC crisis is feeling stuck - financially, spiritually, and yes, maritally. It's a "Is that all there is?" kind of feeling. If you can show him a path to financial independence/ change of lifestyle/etc, he might start to feel less hopeless.
Fourth - various B vitamin deficiencies also cause depression. If you can get him to take a B complex, fish oil, maybe some SamE or 5-HTP, this might also help his depression.
