Tutor Twin Girlfriend

Tae-gyu and Na-yeon have been dating for a year. She introduces her close junior, Ah-joong to Seo-jun. However, Seo-jun who prefers older ladies meets Na-yeon and had a one night stand... Na-yeon comes to ask Tae-gyu for forgiveness, however Tae-gyu was not home, but his twin, Jae-gyu. Na-yeon who has been dating Tae-gyu never once heard of Jae-gyu, and thought he has been lying from anger. However, after seeing the twins' picture, Seo-joon confirms that they were a twin and inevitably believes. Could it be true?