I honestly don't understand the ex fiancee

In the novel it's clearly stated, he hated Nivea since the moment he saw her, because she look like lifeless doll, and when the doll show emotion, it's a love toward him, the more Nivea show affection the more he hated her, so it's not that he didn't realized Nivea love toward him, instead because she loves him too much, it suffocate him to the point he feel disgusted. He know his parent hated and mistreated Nivea in the mansion because of her mother background, he know Nivea parent never visited her even once in the 10 years of their engagement, and also his friend the Crown Prince insulted Nivea every now and then, he himself said unless he is an idiot it's obvious she is an outcast. So it's not like there is some kind of misunderstanding or miscommunication. I wonder where does that regret come from?