You and Heeseung broke up because you "apparently" caught him cheating on you with another girl after your band practices.

It was Valentine's Day and your band had to perform at the Valentine's festival. Your music teacher assigned you to sing Kiss me by Sixpence None The Richer with Heeseung and you weren't really excited singing a love song with Heeseung. At the festival, you guys were backstage preparing. The tension between you and Heeseung was awkward. As soon as you guys were called up to the stage, you guys started going to your spots. Huening kai was on the drums, Jay was on the electric guitar, Ningning on the electric piano while you and Heeseung was on the microphone.