Lover: My Wife's Man(2018)

Stop peeking and let's have a fling. Min-ho works at a private detective agency where peeking into others' lives is what he does. One day, a pretty woman named Mi-na asks him to tail her husband and Min-ho is in for a shock. The man he's tracking down is in an affair with his wife, Soo-kyung. The place they meet each other is usually Min-ho's house after he's gone to work. Min-ho installs secret cameras to catch theem in action and watches the scene with Mi-na.