My Man is Cupid season 1 episode 14
Episode title: Jealousy
Just before his final “metamorphosis”, Sang-hyuk finds out who Baek-ryeon is and feels very confused. After hearing that once he enters the transformation phase, nobody can tell when he will come out, Baek-ryeon fears that Sang-hyuk will disappear forever. Jae-hee happens to see a portrait of Sang-hyuk and So-hee, and he visits Sang-hyuk to ask who the woman in the painting is.
