I think her breaking point was that hospital thing. The one fucking time in their entire relationship that she obviously needed his support for a change, he was an absolute fucking dick about it. I think genuinely started to sympathize with her at that point because he was obviously being an abusive psycho. I also think the hospital and maybe even her co-workers who encountered him in that period may have all just point-blank asked her about his abusive behavior and flat-out told her he wasn't just kind of a jerk, he was actually abusive and she had to get away from him.
Hospitals generally ask questions when a woman shows up and then her SO shows up and is obviously a fucking psycho.