Keep the Secret in the Memory(2005)

Original title: 기억에 묻다

A couple gets a phone call while they are on their way to the train station to go on a trip. Cheol-min hears from her friend that his girlfriend had previously lived with her friend. Hearing this, Cheol-min is worried and does not want to go on a trip. He is very excited by the feeling of betrayal that he cannot trust this woman.