Yes, he kind of fell for him but just in the subtext. At the end he liked him, but it was late for him to be aware. He wondered why he couldn’t kill Yoon, but he was confident to kill Taejoo.
Being distracted by Yoon and slept with him when he was about to fulfill his ultimate goal. And the fact he is confused about being jealous of Yoon or Taejoo.
Unfortunately he never understood his feelings because he was psycho. But he had different feelings for both of them. For Taejoo, it was a destructive obsession. And for Yoon, he wanted to manipulate him but admits he had a soft spot for him and wanted to free him from the stepfather after the revenge.
Interesting
Did Se Hwan actually like Yoon?? Like I read the story, and I'm pretty sure he was faking "liking" him for his brother, but the torture scene confused me