My guy my family is from Japan I know about toxic work culture it's bad but it's really not an impossible situation the way , it's still entirely possible to find or get a new job especially when you have experience.
It's not really naive we know his stated reason but reality is he didn't even try I can entirely fault someone. Saying they both couldn't live together makes it seem wayyy mire equal a split and reason lets be honest 99% of this can be squarely blamed on him.
This is just an aside too and I know japan doesn't see it like this but dating your colleague specifically one working under you is gross the power dynamics at play get murky even if she approached him first he still doing it is gross.
Also by his logic he shouldn't really date anyone he can't commit to a relationship when it comes to real commitment because of work but he can do so now? Even without every else this guys still foul for that imo.
As for going above and beyond, not really he's doing what's expected even by japanese, he's a deadbeat even by japanese standards especially with the more modern standards expecting more than financial support