"What you feel for me isn't love, but an obsession. An obsession you think is love. Lulu, to love a person is to have your heart pound at the thought of them, it's the longing when you can't see them, it's an impulse that seizes both your body and mind."
Gu Yuming wasn't trying to hurt Mi Lu, he knew the extent of her obsession with him. But it wasn't love. She might not understand that now, but someday she would. When she genuinely fell in love with someone, she'd realize that what she was pursuing now was only a phantom not true love.
"How am I immature? I'm twenty-one. I understand, what I feel for you is love. I can't be mistaken, how could I not tell?" Mi Lu wouldn't listen to anything else right now, all her mind occupied with what Gu Yuming had said about already having someone he loves.