Sorry but the story started out to be brother-sister relationship between Ning Que and Sangsang. Even the way their bodies look, it's similar to an older brother to a small younger sister. The story tells of a scene where Ning Que became comfortable of sleeping with Sangsang because she has reached puberty stage. But then since Sangsang told Ningque that she wanted her for herself then he stopped dating other girls. He could just told her that they can't be lovers because they are related to each other by the way they built the relationship. Just taboo in my opinion.