Tutor Twin Girlfriend

Tae Gyu and Na Yeon has 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?
(Source: HanCinema)