My sister in law (Ever Since We Love (2015)

Myeong-hoon usually likes to go to massage shops, where he can even have sex with the masseuse. Then one day, her younger brother introduced him to the woman he would marry, and the woman who would become his sister-in-law was the masseuse he met recently at a massage shop! Myeong-hoon makes a secret proposal to the embarrassed woman, and she accepts it for the sake of her smooth married life, and their dangerous relationship begins.