If you read again from the time they started to meet, won never seduced the brother, he just wanted to get closer to the brother since he is the closest connection to Jinha he could have and he could obviously see that the brother likes him. He just took advantage of that. This is based on how I understood it okay?
And I think why he dressed up Jinha as his brother is because of the guilt? Since he knew he could not love the brother, he used Jinha to at least pretend that he loved the brother while doing it with Jinha.
No..... That's a misunderstanding on ur part... If u remember there was a flashback where won brought a gift for jinha's brother(he was so happy about it) but then he saw won gifted jinha the same thing....
I think it was the coat.... so yeah he didn't tried to dress him up as his brother but as his past self....
So won was seduce the brother and getting close to him to get closer to jinha .. and when he finally got jinha why did he try to turn him into his brother?
Tf is wrong with him