Jessica Edens, a particularly nasty murder-suicide. She killed her own two children and her ex-husband’s (married) girlfriend (who was cheating on her husband) and left a series of notes telling her ex-husband she did it to make him suffer, and apologized to other survivors of her victims. One of her two children was his, also.
I was going to say something snide about the ex-husband cheating with a married woman. I’ll let it go. Even when I was single, I avoided involvement with married woman, especially if they had kids. Once I got married, it only strengthened my resolve to avoid other men’s wives.
Once upon a time I dated a woman who neglected to tell me she was married...
...to a Marine Corps drill instructor.
I always checked marital status after that!