but... but... true love!Yeah, I mean, if you really think about it, none of this make sense.
The thing is, the general story structure works fine-ish when it's the heroine, from humble origins, being harassed by those in power. In those cases, you can see a prince who disavows his high-born but rotten fiancee to marry the heroine for her kindness, "saint power", or whatever bollocks, a classic fairy-tale-like progression.
Flip it around and you get absolute stupidity; like a prince pissing off a duke and spurning his daughter with a half-arsed excuse/accusation so that he may marry the daughter of a viscount as if they were of the same rank, power, and influence. Generally, the progression of nobility is Knight > Baron > Viscount > Count > Margrave > Duke so prince Peabrain here is choosing his affair partner instead of the daughter of her father's superior's superior's superior with nothing to back it up. Whichever way you want to look at it, these are just story contrivances with dumb people being dumb just for the sake of story.
This is exactly why I loved the early parts of "Duke's Daughter" so much, basically everyone outside of the "heroine's" harem realized how absolutey scummy the male leads were being and even her own brother was heavily reprimanded, the knight commander's son was beaten and forced to go throug hellish training becuase not only did he go against the daughter of a duke, he laid his hands on her as a knight, etc. I think only the foolish prince didn't have any direct repercussions? I know his downfall at the end wasn't very satisfying imo.