Discovery of a Hopeless Relationship

What is the probability to meet someone you hate? At a OT, Yoon Woo meets Jae Won. Jae Won says that they met in past, but Yoon Woo cannot remember. He only can feel familiarity. Jae Won continues to try to avoid, but Yoon Woo continues to pursue him as he is curious. What exactly happened in the past?

Original Webtoon:
R19: BookCube, RIDI, Bomtoon, Lezhin, Naver Series, MrBlue, Qtoon
R15: KakaoPage, RIDI, Lezhin, Naver Series