After reading the comments, questions and answers, my gut tells me, your Dad has spent his life doing what was expected of him; man of the house taking care of material needs of others; spiritual wife, family, job, house, etc. Now he is feeling depleted and needs to take care of himself. However, he is still obligated by the needs of others. Depression often occurs when you are stuck between rock and a hard place; tires spinning in the mud.
His situation is not easy to change. If gets up and leaves to find the new me time, he will still need to work to support one house, plus other living arrangement for the new me. Working two jobs may not allow the extra free time to explore these other options. His life is simpler where he is, but within the context of dad and husband, the new him is harder to realize, since it can be disruptive to others who depend on him.
I can sort of understand since he sounds like my own father, who worked hard each day, year after year, always home after work for dinner. He constantly had the pressure of supporting an ever growing family, that had its ups and downs, with little private time for himself beyond just sitting quietly or reading the paper. As the years passed, he would come home stressed, to another place of a different set of home stresses. He seem to make it through, but with less and less smiles as the years passed.
He changed after he retired, when he was able to remove work stress and have more free time at his home; hobbies. My guess is your dad needs some free time, at home, which is not perfect enough to recharge, due to work. it sounds like he is not ready to retire, but my guess is that when he does, he will smile again; his male mission is completed.