He had a psychotic break. He was broken. He isn't the one that killed the other so-so number of girls before... He was trying to survive. He wasn't the one who beat him & played mind games.
Remember the time he tried to escape? No one helped & he was beaten & carried back in KICKING& SCREAMING.
Imagine crying for help & no one does? He lost it.
Then that DRIVER DUDE just let's two people land on his car & watched one wail on the other??? You know who the other psycho is???
THAT DRIVER.
That driver is out THERE getting his rocks off on watching victims getting dragged around by psychopaths without calling the cops...
Also
... . What if Bum DIDN'T do it? You think Oh was gonna be chill & let her live? Or Bum was going to over power Oh with his mad skills in martial arts???
Yeah, Bum leg sweeps Oh & grabs her & saves the girl like a t.v hero. Cause victims with smashed legs do that, right? Why isn't Bum kicking the knife from Oh's hand & throws it at him with the mad skill of Black Widow????
... although if that stuff did happen, this would have definitely taken another turn.
Why are people crying over Sangwoo? He was a murdering psychopath and Bum is an obsessed stalker. This isn't romance this story would never have had a good ending. It is dark and shows the realistic side to how this ends. Defending Sangwoo for his actions because he was abused is flawed logic. Bum was abused too and he never had the intent to murder anyone. I enjoyed the story as it was a fresh new plot but not once did I think they were in love or that they would get away with this. Not once did I believe that they didn't deserve what they got. Rehabilitation and therapy for psychopaths is only an option before they go on a murder spree. The ending may be left with loose strings but that's how reality would be. Justice doesn't always prevail and we don't always find out the full truth to things.