I’m going to take a wild guess, she discovered him cheating on her with someone serious. (Serious to her, that is.) Maybe a long-standing affair right under her nose; maybe a high school sweetheart; or some such thing that hits Michelle in the pride.
As opposed to something she knew about and tolerated.
For most other crimes against the spouse, said spouse is usually very forgiving, given all that’s at stake.
It’s betrayal and the wound to one’s ego that makes a person openly bitter and vindictive.
Probably the cook. She took care of that!
If he stays with her after this, he’s a simp and a cuck.