Love and War: 12th Man (2008)

Original title: 사랑과 전쟁: 열두 번째 남자

Danyeon and Hyeongpil are a married couple who have been in a bad marriage for many years due to a lack of sex. One day, Danyeon learns of Hyeop-pil's affair through a phone call from a stranger, and in revenge, she has affairs with 12 different men.