She is too hard on herself, relationships aren't a one gate play, they require both partners efforts. So, prince is more at fault then her, he was most probably less busy than her(enough to flirt with other girl), and had more authority in their relationship. And why does Euphie even question whether she hates the princess, for what exactly can she hate her?
And, honestly, I have expected stones encrusted into the pommel. Maybe they could have even made the pommel shaped like six-pointed star(don't know how the actual construction will fare though).