The past of the cool kid bullying me?

Yeon Doo's stalker forces her to go home with him but luckily, her friend Yu Na repels him. They run into Hyun Ho and he offers to take Yeon Doo home. Hyun Ho asks her relationship with Ju Ho but she tells him that they're only classmates. At school, Seol couldn't stand seeing her friends taking care of Yeon Doo and not her. She finally explodes.