So, I went and found the novel and read about 160 chapters before pausing. It does ease up later, but the ML is still the same - possessive, to the point of ignoring what the FL would want, but at least she doesn't make it easy for him (though she does give in every time when they're intimate). Also, I stand by the best friend being in love with her being pointless. So far in the novel he's had several chapters, and in every one he just mopes about the love of his life being engaged to his boss and childhood friend.
Also, I'd like to defend her dad a little. FL tends to act a bit out of the norm, so dad thought the crown prince, the most perfect man in the empire, also the most powerful next to the king, would keep his daughter safe/tolerate her craziness. He'd actually been considering breaking off the engagement because she hated it so much and the prince didn't seem into it, either when the cp suddenly comes to him and swears up and down he'll love the PM's daughter.
Well, a devoted, obsessive, slightly yandere ML isn't for everyone, but I don't mind it so I have nothing against the ML. But he also doesn't really care about the FL:s opinion in a lot of matters, and she gives in too quickly. That title is a lie, in ch6 she just decides to go along with it after finding out about the flower seal.
I don't know why the author/artist thought it was necessary to include her friend being in love with her, honestly. Those were a couple of chapters that went nowhere and had no meaning to the story (this far anyway.)