They'd broken up a couple months ago because he was being abusive. She was in her new home with her new boyfriend and the thug had some crazy idea that he'd break into her place and propose and then they'd get married. Instead, he found Mack with her new boyfriend and proceeded to assault both of them (I haven't heard what kind of injuries the guy got) and attempted to kill Mack.
The psychopath needs to be locked up for a long, long time.