In That Relationship summary:

Do-yeon, who grew up together with her Childhood Friends, Won-young and Won-hyuk. Do-yeon, who had been thinking about Won-hyuk since childhood, made a public confession to Won-hyuk on the middle school festival day, and was dumped. Slowly, the relationship between the three ends when the twins immigrate abroad a few months later, and the public confession case remains a dark history of their lives. After a while, Won-young, who returned to Korea without notice, appeared in front of Do-yeon and confessed…