Could be MLC, drugs, booze, a psychotic break, an act... who the heck knows. And you know what? Doesn't matter. You're never going to figure it out. And he is NOT your problem anymore.
I, like the others, am concerned about your finances and the potential fallout on you. Continue on your path. Additionally, have you documented this incident with the children? I am very very concerned about their mental state given the way their own father treats them. He can sue for custody if he's interested in donating money to his lawyers, there's no way he's getting them. But it's more than that. These types of interactions are no good for them. What are they saying to you? How are they feeling?
I am so sorry NLW. Put your game face on. Continue being kind. Keep those hands clean. I know you know all of this, but the reminders are helpful
