Hyunjin was your obsessive ex-boyfriend. You were in a toxic relationship. He was so obsessed with you. He would manipulate you.He was even jealous of your friends. If you got even remotely close to any guy,he would get angry and yell at you and get very angry

A few people at school and your friends told you that you should break up with him.You break up with him

But he couldn't stomach it and sneaked into your house at night and went up to your room.You locked yourself in another room