Can someone remind me what that girl did to Yoonbum?

When they were in high school together the girl had stopped being friends with bum because bum told her that they were dating when they weren't. when she heard that out she stopped being friends with bum. bum tried to figure out why she was doing this but she just kept ignoring him. So bum would take things of her to calm him down. then she found out that there were still rumors about them dating so she confronted bum. Bum saying how that the guy she took an interest in doesn't like that it's only for her body. Bum was saying how that he likes her for who she is and even the scars that her father had given her bum thought they were beautiful. When she heard that she snapped. She grabbed a drink and poured it on bum, telling him to just die, to disappear and etc. thats what broke bum and also the reason why bum killed that girl in the basement because he thought it was the girl from high school

She is the high school girl Bum liked, she was being abused by her father and Bum noticed that (she had wounds in her wrists) since he was abuse himself by his uncle. So they started to be "friend" if i can say it that way, and one day her father stopped doing bad things to her and she totally ignored Bum even when he tried to talk to her through a letter he puts in her desk and when he asked her when was she going to answer, she just kept saying "next time". Tt that time Bum thought they were together, so when she found out about that, she screamed at him "go die, fucking pervert", that sort of thing. Bum s really chocked, being told to go die and stuff like that by the girl he liked and supported when she was abused by her father, it traumatized him, and that is what sangwoo mentionned