Moonbyul doesn't know that Jin has a FFI or what we called Fatal familial insomnia. Jin wants to keep it secret because he doesn't want to bother her, Jin doesn't want Moonbyul's problem to get worse. Jin has been hiding his pain for a long time but why? Because before he died, he wants to disappear from Moonbyul's life that she doesn't know about. But his plans failed, Moonbyul already know. What is he gonna do now?