I think it came from a oneshot compilation in which yongsun graduated from college and already working but byul is still studying so yongsun's friends are kinda wondering why yongsun still want byul despite she has a lot of 'already working' suitors and then yongsun became worried because she hasn't seen byul and talk to byul for a week turns out that her uncle was sick and she had to help her uncle on their business.