Nice Sister-In-Law (2015)

“A man in love with his sister-in-law can't stop fantasizing about her.”

Ha-yeong is a successful psychologist. One day she gets a secretive request from her sister Ha-joo. Apparently Ha-joo's husband Woo-seong is refusing to have sex. Ha-yeong agrees to be their couple therapist but finds out that her brother-in-law actually has sexual desires for her and not her sister...