Scared can't begin to describe how Hyejoong feels when he came back, begging her to take him back, Taeil walks in on the whole thing, she tries to pretend like she imagined the tears and hurt look on his face when he saw the sight in front of him.

She wants him to leave so she could explain who he was to Taeil, no matter how much she begs him to leave, he wouldn't give her up. Taeil doesn't understand why it hurt so much to see someone else confessing their love to her. He doesn't want to understand why. 

He just wants it to stop hurting.