I miss you

You've been friends with Park Chanyeol like forever.He was always by your side. But he had to leave you because he had to train in SM. Your attitude changes because of this.
One day these 12 flower boys came to your class and one of them was Chanyeol. He doesn't really remember you but Chen helps you try to get Chanyeol to remember you. At the same time Chen tries to get your memory of him back.