The ML is extremely possessive and jealous. He has been in love with the FL since they were children and would do everything to keep her by his side. Everything with the heroine is a misunderstanding. He spends time with her because his friend is in love with her and he has difficulties rejecting her because he as the prince has to be courteous. In the original plotline, the ML fell out of love with the FL, because she out of jealousy was mean to the heroine. In this plotline, the FL endures the provocation of the heroine and this allows her to keep the ML.
ML: "If there is any man around you, I want to kill him. And if you were to choose any man other than me, I will kill all of the men you chose, so prepare yourself" (v1c3).
The existence of the original plotline makes me hate the ML. And our insight in his possessiveness makes me hate him even more. If his love for the FL is so strong, then how could her display of jealousy be enough to make him abandon 10 years of love and marry another woman? Why is he allowed to kill all the men around her, while she can't even splash tea at the heroine without falling out of favor? Besides, he knows that the heroine provoked the FL to act that way. In this plotline he is even surprised that the FL is able to remain calm.
All the female enemies of the FL are favoured no matter where they go, because of their beauty.
The FL later on becomes stunningly beautiful, but all she gets are more enemies.