@Suckerforshipping: Being raised as crown prince did that to him.
He NEEDED to be successful, be at the top, because he's to be the king, that's likely all his teachers told him, directly or discreetly.
But at the same time, because he's the prince, whatever he say, go.
The way he treat Aileen is basically the result of that.
He treat her like his 'thing' because he's the crown prince.
He 'dislike' her being successful because it reflect poorly on his own perceived imperfection.
And so, unlike Aileen who's busy trying to polish herself into that perfect queen candidate, the heroine fawning over him feed into his ego (even though in truth she's just using him for HER own ego) and made him chose the heroine over the less responsive Aileen.
But because he still think of her as his possession, when Aileen did not cry and beg for forgiveness, and instead went and got Claude, the 'better one' in Cedric's eyes, it hit his ego HARD and made him hold grudges.
tl;dr? The pressure from society combined with the lack of anybody to tell him how to treat others with respect made him into egoistic manchild who demands adoration of others but always treat others as 'below' him.