Did the father really disappear on purpose to hurt his ex bully, though?

We are told so from the mother's pov, but she is not exactly stable.

I dunno, I find it hard to believe that someone would ditch their entire life (all non-wife-and-son relatives, friends, job, possessions including the house, and any chance to make something of yourself ever again because Japanese society is all about your personal history), when simply ditching the wife after making her fall in love with you would work pretty well as revenge too. Especially in Japan, where traditionally women over 25 are considered past marriage, so she likely couldn't recover from it.

It's left ambiguous, but I always assumed something bad did happen to him.