Jay is your ex. He was your boyfriend for 1 year. However...recently you guys broke up secretly. You guys broke up for a reason.

Sunoo, Jay's best friend has a girlfriend named Lia. You have a crush on Sunoo and Jay has a crush on Mia. So you guys break up and work together to help each other. Jay helps you to win Sunoo's heart while you help Jay to win Mia's heart.

However, no one knows that you have broken up. That's why you guys still act like a couple in front of other people