I like him. I think he's just dealing with a lot of insecurity because of imposter syndrome. Obviously that doesn't justify treating people like shit but I appreciate that he's self-aware and makes an effort to treat Gallion better. I think he turned out alright considering he never had parental love and when his real mother came into his life, all she did was try to manipulate him. It'd be weird if after going back in time he suddenly became this well rounded guy. Therapy would do wonders for him
Honestly, you probably won’t. From what I’ve read of the novel, he’s the kind of man who only really looks out for himself and prioritizes his own interests. In that sense, he’s realistic; most people aren’t heroic manhwa protagonists willing to sacrifice everything out of pure kindness. Most people would act more like him. I don’t like him at all, but it does make me wonder if I’d make some of the same choices, since it’s human nature to want to survive.
You don’t need to like him. Honestly, for me, it is more of “I don’t agree but I get it. I guess the mc felt human to me. He is selfish and seek survival. If it was me, I would do that too. Spoiler:
In his last life, his mind also got corroded by drug. His actions of course are completely on him. But in this life, his mind is clear so he made better decisions to survive, and he stay away from the people who will give him drug. He is cunning and calculating. His ultimate goal in this life is to just seek immunity from the empire, and eventually leave while gathering all the wealth from the trade he established. The informations he got from his previous life help a lot too, and he effectively use that to his advantage.

At what point am I supposed to start liking the mc? Please tell me he gets better...