What's Wrong with Secretary Kim S01E12 - I Don't Want to Waste Away Tonight

Young-Joon stays at Mi-So's place, but Kim Mi-So can't seem to relax with him in bed so she's trying to do all other things instead. Eventually, they decide to go to his place because it's much bigger and has multiple rooms. But Young-Joon is still worried and decides to stay next to her and ends up singing her a lullaby. To return the favour for a good-night sleep, she decides to make him a breakfast. More is revealed about Young-Joon past after the incident.