It was disgusting. Why should he marry a woman that doesn't even understand how hard he had worked and yet just reaps from the fruits of his efforts and then ruins it?
Claudius thought that marrying such a woman would only bring nothing but trouble to him. Their dukedom might just fall into pieces in her hands.
He thought that she would learn and mature a bit as she grows up. But even after three years of observing her secretly, he didn't see any change that would convince him that she would be a good duchess someday.
Claudius gave up on believing in her and just decided to ignore her. He would bid his time and look for a way to cancel the engagement.
Moreover, he had been going on expeditions and battles when the King ask for knights. And in those expeditions, Claudius discovered that there was so much more in this world than being his father's obedient son, pleasing his parents, or becoming the duke.