My Brother's Girlfriend (2018)

Original title: 내형의여자친구

Sang-min is living in Hyung-min's house. One day, Hyung-min brings home his girlfriend So-mi and says she'll be living with her. So-mi looks younger than Sang-min and he witnesses his brother impose physical violence on her. Actually, Hyung-min had brought her home because she had nowhere else to go after the stocks crashed and he was paying off her debts. She'd put her hands on Bitcoin once again and he was only trying to persuade her out of it, but Sang-min had gotten the wrong idea. So-mi was sad and drunk and Sang-min ends up having sex with her. Hyung-min witnesses this, but pretends not to know. Sang-min slowly abandons his girlfriend, Jung-hyun, who comes to his house because she can't get a hold of him. Alone at home, Sang-min tells her about his relationship with So-mi and makes a secret suggestion.