Tao Ran was actually very anxious that Xu Yun had a bad impression of Ke Yuan. And as per the novel’s plot, Xu Yun never expressed her love for Ke Yuan, and under the question of the little sister, she lied with a guilty conscience that she didn't like Ke Yuan at all, but in fact she hated Ke Yuan.
This happened to be heard by Ke Yuan who secretly sent Xu Yun home, and caused him to be extremely sad. And this resulted in him being with Huang Tao for sometime. Ke Yuan knew Huang Tao's feelings for him, and asked Huang Tao if she wanted to be with him. How could Huang Tao refuse? They were lovers for a period of time.
Later, Ke Yuan realized that he still couldn't forget Xu Yun. He regretted being with Huang Tao and broke up with her to stay true to his feelings for Xu Yun... This caused Huang Tao to completely blacken since then, although the role of the vicious female partner in the plot was to create trouble for the hero and the heroine and in turn promote their feelings for each other.