Responses

That's actually a good question because he can leave now, but even tho he resent his mother he still thinks she loves him maybe not more than that evil twin but he think he's her second priority . He still doesn't know what that dead bitch planned all along for yeongwoon and how his mother purposely kept then apart. He maybe feel some sort of connection. He also probably had nowhere to go because he thought yeongwoon is gone too. He can actually leave right now though.
He didn't abandon him. Yeongwoon did not abandon Seo in. He tried, he really tried saying his goodbye's 10 years ago