Why are people hating on the cousin? Yeah, he's rather brash, but his heart is in the right place. Just cause he's suspicious of the FL doesn't mean that he's wrong to do so. He literally explained his reasoning.
Every other duchess in history was brought in BEFORE being aware of the curse. And they were forced to bear children after being wed. She's the ONLY one that was brought in despite knowing it. Currently, he hasn't met her, has no idea of her character so far, and isn't completely privy to what she had done for the place.
But we see that he's a bit of an innocent kid. Like, he's told to do an assignment by his cousin, and despite stating multiple times that he won't do it, he then spends the night trying to find the book.
All he needs to do is come to understand that our FL is a good person at heart.
I feel people are way too much into the FL and just hate anyone that is even the slightest bit opposed or suspicious of her.