I know bits of it but I still have no luck in finding it!
It starts off with a girl who works at a flower shop. She sees a boy and he immediately makes her his lover. (I think he was a demon).
In one of the chapters, the boy is going back to his home so he can finish his work. He takes her to his private beach house, where he makes love to the girl and she allows it. The next day, they get dressed and he notices how much he changed her. When they get to the airport, he gives her his earring he always wears and tells her that he will come back for her, then he kisses her and leaves.