The romance between angelica and the price was honestly quite tragic, more tragic than most of the intended so called love tragedies.
worked within framework of royal rules, yet her love only served to oppress him more leaving his repressed feelings to fester into a ticking time bomb.
Others might blame the prince for this but from another perspective, angelica might've been so diligent herself that she never gave the prince the room, chance or opportunity to confide with and truly relate to her on a more personal level, and that disconnect eventually turned her into, in his eyes, the personification of all the implied responsibilities that came with him being born into royalty. Even if leon was totally right about him, all this still seems plausible and it doesn't really imply anything about his innate chracter when you consider that he was just a kid.
In spite of this, angelica still worked her entire life to become someone worthy of him, but in the end lost to actual, honest to god fate, to a god-like rival with perfect information. And she still would've been fine with him ending up with someone else, probably, anyone who's not a cunning, reverse harem scheming literal player who doesn't even believe in the same "true love" that the other two do. Then of course there's the standard "she still liked her anyway, and he sort of liked her still does but is too committed to another now to even pull off the mistress route" devdlopment to seal the deal.
If the mob hadn't intervened the events would've taken an even more tragic turn. And this all happened because someone was toying with their relationship in the palm of her hands, like it was just a game.
As an aside, this line "decided to ... while overlooking a very important fact" kind of applies to the armchair writers and part time manga "critics" you find anywhere, who are just eternally perplexed as to why authors keep using or avoiding a certain trope or writing decision over and over again, or that they don't do it enough. Who knows, but it's good to keep in mind that authors who write their specific story the exact way you want them to would probably end up making something that's disliked by most (and maybe even you), and you wouldn't even know because they'd be axed or left untranslated.