Read Swim in the Cherry manhwa 18

During his innocent and ignorant high school days, Suyeong had a very awkward first kiss with his first love, Chaeri. Before he could resolve the misunderstanding, Chaeri transferred to another school, and years passed by, with his first love buried in his heart. After completing his military service, Suyeong goes to an opening party and encounters Chaeri, who had come in as a transfer student. Chaeri’s advances sway him and he realizes he’s in for a surprise…

”What would you do if I allowed you to make up for it?” 

“You started it first.”