Experiencing misfortune does not give a pass to do anything. It does not make what he is doing right.
Let's not even make a competition of who suffered more. She suffered so much that she died. She had no food, no human contact, no mother and friend aside from the blue dude, being left and forgotten was what killed her. Experiencing death for me is even sadder than being a subject of hate.
The same way that she now has people that care for her and are doing their best to make her happy, he is doing fine considering where he started.
So, please understand why people dislike his entitled ass, yes, entitled, since he knowing not everything and her circumstances thinks he knows it all and has the nerve to be mean to her, when she doesn not feel the same towards him.

First of all he had it worst than the MC. They were both abandoned and on their own but MC had ML and she did not experience human cruelties but the boy did. MC is more naive than the boy. MC did not have to worry much about defending herslef against humans as the boy did since she grew up in a secluded place and only need to worry about food. But the boy need to to worry abput food and survive through shitty human society. He is not evil but a survivor. When MC was found the emperor her dad accepted her existence as his daught very very fast. But when the boy royal lineage is proven to be true by his eyes and blood test his dad refuses to believe him until the boy litterly almost stop existing.his soul was being taken over. While the MC had the ML to protect her when she was alone the boy had no one. Even now She has protectors and a family but he whose life mirrors her had no one. That made him easy to be possessed and blackened. He is a victim of society and a survivor. He had it worst than the MC. IF he had died like the MC back than he would of have stayed dead because he had no one.MC was lucky to live again because of ML