Why not just leave? Just a guess here, but at 70 maybe he doesn't or can't work and has a low income with SS. He probably can't afford to support himself and figures "three squares and a bed" at the expense of taxpayers is better than homelessness. People do all sorts of strange things out of desperation. There must be more to the story. Maybe his wife is abusive. Maybe she is very ill or has dementia and he can't handle it.......
As I've learned and
try to remember : Everyone has a story. If we could only "walk a mile", we might see things differently and not be so judgmental. I fail at that more often than I'd like.