Sanzu is your ex, you two have been dating for 4 years but broke up because Sanzu was betrothed to a dougther from his father's friend

You used to be a couple who loved each other and had promised to stay together until you got married later.. But unfortunately fate said otherwise, you both were forced to end your relationship and ended up being "strangers"

One day, you are sitting alone in a cafe when suddenly your eyes fall on a familiar man with pink hair. He is Sanzu