Yusuwa Gachi

Yu-Su's first love is his childhood neighbor, Cheong-U. His feelings are discovered by Cheong-U's little sister, Ji-U. Ji-U proposes to the flustered Yu-Su that he become her boyfriend so Yu-Su can see more of Cheong-U. Despite to his initial hesitance about his feelings, after seeing Cheong-U again for the first time in years, Yu-Su becomes desperate to get closer to him...

(Source: BOMTOON, translated)