Seo is your best friend since kindergarten. The two of you always spend time together. Every new thing he did will always involve you. This special bond you have with him is something you don't want to lose. Even with a cost you will have to hide your feelings for him forever.

It hurt you seeing him going out with other girls while you could only hide your feeling for him. You thought you could hide your feeling until one drunken night which lead to change your friendship with him forever.