Let's talk about canonical Sebastian
For some reason Sebastian got a reputation of another dark Slytherin who's obsessed with power. Many added him to ✨the Slytherins✨ list. Although in fact he's nothing like Draco, Snape and especially Voldemort. So let's forget about fanons where he's obsessive and possessive and remember some FACTS about him. All based on his behaviour in the game.
He's a brilliant student. Professor Weasley and Scribner both said it. And teachers don't usually praise you for nothing;
He's the BIGGEST NERD in Hogwarts. "What I do with every book. Read it." Had me. He also mentioned his parents tought him to love books. Dude goes to the restricted section not to become another dark lord, but because curiosity in his nature;
He's loyal and protective. I don't even beed to comment on this one;
He is full of youthful maximalism. Which is completely normal at the age of 15. That's why he thinks he knows better than anyone else and hates ALL the goblins just because one cursed his sister (as he thinks);
He expects everything from his beloved. But just because he would do everything for them too. Like risk his life and soul to safe your life? So he doesn't use people, he just thinks it's normal;
He's understanding and supporting. Yes, part of him saw mc as someone who can save his sister. But he only mentioned it once or twice. Beside of that he saw them as partners. When mc said they can't tell him their secret, he understood. He didn't push or try to trick them into telling him. But when they decided to share he was nothing but supportive (although he didn't understand a thing);
Again, he's like super smart. Reading books isn't enough. He actually taught himself the unforgivables and could decrypt Slytherin's book;
He has a healthy self-esteem. He knows his worth and don't have a need to prove something to someone. You can see it in his reaction when he lost in the duel. He doesn't shout about how cool he is (cough Leander cough);
He knows exactly what he wants from life and does everything to get it. Like a good Slytherin he is;
He's not even violent. You heard him screaming? Me neither (expect this one time with Solomon but oh well). Usually he just says he needs some time to think and calm down. He's very mature (If not for his maximalism, but it'll pass). At least more mature than any grown up I know. He only called mc "arrogant", but never screamed or bit anyone.
That's just a few things I could think of! Sebastian is not only cocky boy, who would kill anyone to protect his family. He's a kind, decent person, who only tried to help. What happened was Solomon's fault and not Sebastian's. He was only a child, after all. It was Solomon's job to protect and support them. And he failed.
