Actually, I think that this time is different, I agree with the asshole of zeus, but in this manhwa is more a one-side love, the blond girl who "loved" the crown prince that would be the present king, he treated her "coldly" because she thought (according to the implicit story) that her status, her own person and her love for him was enough to make him love her, when he was just being forced to accept those feelings of her (and the good background of her family) and when he fall in love with the brunet girl and brought her in, the other girl delusion/fantasy fall off, THEN she, having oppressed him since childhood with her "love", broke into rage and did blame the brunet girl and her innocent child (the little girl that also was imprisoned).
Sorry, I don't remember names, and also I don't think that was a cuestion of loyalty, the actual king was young, didn't have the enough power to deny the blond girl advances and the interested nobles.
I think that was a matter of tragic lives that collided in tragic ways
So basically just like with Zeus in greek mythology this tragedy could've been avoided if the emperor was loyal and did not stick his stick where it didn't belong.