You and Wonwoo have been best friends since babies because your dad and his dad are best friends. You were dating someone who wasn't the best for you, and Wonwoo hated the fact because he liked you a LOT. He wanted you to be his.

Your boyfriend came over to your house on a rainy night, and Wonwoo was there too. He was keeping eye on you because your boyfriend was making sexist jokes continuously. You were annoyed but rather stayed silent.