Love and Affair (2011)

Original title: 사랑 그리고 불륜

Eun-kyeong introduces her elementary school friend Mi-hee, whom she met after a long time, to her boyfriend Ji-hoon. Mi-hee, who is currently dating a married man, feels attraction to men who are in relationships. One day, they get a chance to be by themselves in the car and she tries to seduce him. He makes her promise that she won't tell Eun-kyeong and wants her too. They meet again a few days later and promise to continue meeting up, enjoying their secret affair. She looks at him with pleasure, at the way he's surprised at the phone call from Eun-kyeong and is blabbering away an excuse. Ji-hoon completely falls for Mi-hee but she tells him goodbye for the sake of Eun-kyeong. Unable to accept this, he goes after her...