What a Man Wants (2018)

Set on Jeju Island. Seok Geun, a previous roller coaster designer, is now a middle-aged taxi driver who is married to Dam Deok. Seok Geun cheats on his wife regularly but still loves her.
Meanwhile, Seok Geun’s younger sister, Mi Yeong, is married to Bong Soo, a serious man who tries to be faithful despite women’s temptations. The couple runs a restaurant, but it isn’t doing very well. Moreover, their sex life is lacking.
Seok Geun tried to convince Bong Soo to cheat on his wife to enhance their sex life. Bong Soo doesn’t understand his brother-in-law ways of life, until, one day, he meets Je Ni.