"No matter how pretty Evelyn was, she had always been ugly to Chester because of what her family had done to him.
He could never accept Evelyn as his wife, and he kept longing for the love they made him lose.
Seeing Evelyn constantly reminded him of it and of the fact that his siblings' lives were in the hands of the Leonharts," Alwin continued.
With the Leonharts able to eliminate the first prince and create their own story of his death, Chester knew their threat was not empty.
They could simply eliminate him and manipulate his younger siblings next. Or kill one of his siblings to teach him a lesson if he didn't obey.
Chester was not a vile person before.
He changed and became what he was after what the Leonharts made him experience.
This was why Chester made Evelyn who was the only Leonhart he could harm, as the outlet of his frustration and despair and tormented her.
When he was violent the first time and Evelyn did not tell anyone, he was emboldened to do it again.
