Yun Yi Yi is 13 years old and accused Chu Fei Yang of ruining her because she's completely impulsive, as most 13 year olds are psychologically (*insert over used excuse that people in the past age differently* No, there's no proof of that. There never has been.). Yun Yi Yi was clearly marked as a spoiled girl from the start, of course she would do this kind of thing! As revenge, Chu Fei Yang has her marry her rapist, and her rapist takes full advantage of it. Chu Fei isn't a saint, I understand that, but the thing that made him believable was his levelheadedness. He knew who the real targets were.
The argument that could have been made was that to get revenge on Yun Yi Yi's father, he had to sacrifice Yun Yi Yi. But the author makes it clear that YYY's father doesn't care for anything other than his reputation. They both could have easily have been exiled.