AGYEONUI BALGYEON

What's the probability of meeting someone you hate?

Yun-U meets Jae-Won at an OT. Jae-Won says they have met before, but Yun-U can't remember him, he only feels a vague familiarity. Although Jae-Won tries to avoid him, Yun-U continues to pursue him out of curiousity. What exactly happened in the past?