Secret - Sikeurit (2009)

Sung-ryeol is a detective in charge of violent crimes. He is an upright man, but is having an affair with his colleague's wife, and it is the reason he loses his own son in a car accident. Wracked with guilt but unable to explain to his wife, Ji-yeon, what happened on that day and why, he loses her in her grief when she decides to go abroad. Ji-yeon comes home unexpectedly and insecurely one day, peaking Sung-ryeol's curiosity about his wife's behavior.