In my opinion...
I think he fell in love with aristia' mother (not that kind of love, just motherly figure as the mother treat him with love)... back then he didn't know about aristia I guess, based on what I read a lot of people seem to like Aristia's mother, and then she died, Aristia come into the picture. Looking at the story, it seem like the prince try his best in everything that he do.. but people around him (etc: king, minister) always praise Arisitia and he started to hate her because of that. This is the start I guess.... and the hatred just increased day by day, Aristia personality is quiet and seem cold, so he didn't try to get acquainted with her. Furthermore, she is engage with him, that make it impossible to get away from Aristia shadow.
I don't know how to explain further, for me I can understand why the prince behave like that. It just like anything you do didn't get acknowledge but somehow, anything she do is been praised anywhere. So he might have develop some kind of complex. Even though killing her child and framing her father to try to kill his child with the queen is quiet absurd. But if you hate someone, anything can happen....
But now, he started to interact with her, so maybe he will develop some kind of feeling to her over time....
My honest opinions: you don't treat a person that way even if you have an inferiority complex,
Secondly, he tried his best, she tried her best, she just so happened to be better at everything administrative, he had a choice to pursue something athletic and be better at her than that, but nah he didn't do that, instead he decided that ignoring her and giving her that sort of treatment was better
Thirdly, if you treated someone like your mother, you'd fufill her last wish(with aristia mother, it was taking care of tia, which he DID not do)
Imo, he wants to be a girl so much that he despises the heroine. He's Such a dumbass
Was rereading this shit. For the 7th time, i just realized that he said she took whatever he couldnt have. Does this refer to aristia's mother, and if it does, does it mean she is indirectly the cause of her death?
And i still do NOT understand why he treats her so badly when he was okay with the mother... -.-...?