It's sort of implied that the husband was abusive, so i don't feel as bad for him as I probably should
A wealthy man married to an accountant is probably a corrupt businessman to begin with. But when she refused to help him evade his taxes, he divorced and screwed her out any alimony. Yeah, he was a vindictive narcissist.
Of course that means that Yukari was already being stalked by creepy mom. And the latter plotted to kill the ex-husband after she found out about the divorce terms. Creepy mom is essentially a Dixie Chick (Goodbye Earl) crossed with Morticia Adams.
