beta
I'm betting that the older brother had a thing for Seo-in and Yeonwoon caught Seo-in kissing him as a "if you do it once, I can give up" thing and it freaked him out. And of course, the older brother probably committed suicide, the poor guy, because he couldn't deal with someone knowing or just couldn't handle thr rejection and the feelings he had. That's probably why Seo-in dyes his hair blonde as well. As a reminder of the guilt he feels is necessary to carry around about his brother. Although, I am wondering if the brother was adopted because of the blond hair. I really hate the blond hair on him. It doesn't suit him at all.