Cheaters (2007)

Original title: 내 여자의 남자친구

Seok-ho, a self-styled playboy with a beautiful wife, is fooling around with Ji-yeon, a voluptuous photographer, but pines for Chae-young, a college student who appears to be the most virtuous girl in all of Korea. But it turns out that Chae-young, who frustrates her suitor at every turn, is not so chaste after all. The plot thickens as Seok-ho's best friend Young-su, outwardly awkward and shy, sets his sights on Ji-yeon, not realizing that she is already involved with his best buddy.