No one keep him in the dark, he just doesn't want to listen to anything related to the FL, he doesn't even bother to think why her parents never visited her even once during 10 years of their engagement, that's why he said so 'unless I'm an idiot, it's pretty obvious her family neglected her' and he did notice you know, he knows his own parents treated her like shit cause her mother is a maid, but he justified their action cause they are a 'Duke family', that's why he never said anything when the crown prince badmouthed his fiance, he only surprised at the party cause the count family dare to ridiculed the FL even though her mother is maid but she is from the marquis family.
LIKE HONESTLY WHY? Why did everyone keep him in the dark about what was going on with her and WHY IN THE HELL did he not notice it. I know this is probably gonna be some cheesy love triangle with him probably trying to win her heart back, but with what she went through I don't think she will be swayed.