My Boss is My Ex summary:

Gomshin was happily dating Yeonha who’s 5 years younger than her. But when he enlisted, Gomshin started to worry about her future and decided to break their relationship, without knowing Yeonha’s true identity. 4 years later, Yeonha is becoming her boss and now looking for a revenge! What’s going to happen next?
Yeonhaui Gomsin / Bosu wa Moto Kare-kun / ボスは元カレくん / 연하의 곰신