The Man Next Door(2010)

Original title: 이웃집 남자

Sang-su (Yoon Je-moon) is an ordinary real estate agent with a wife and son. He also has a pretty younger girlfriend, but still brags to friends about his latest one-night stands with other women. Money and sex mean everything to him, but just as he fulfills his dream of driving a Mercedes-Benz, things go awry.