Responses
Because he's a plot device who was literally created for the purpose of getting between Yahwi and Jooin, add some drama to the story, and force the two to realize what they really want.
The only way to "free" him from being a plot device in Jooin and Yahwi's love story, is to remove him from the story.
Til the end Cain is portrayed in the most pathetic way. Yearning for someone who doesn’t even think about him ever. It’s really unfair that this WHOLE CHAPTER was about Jooin. Like they made the Yahwi chapter about Jooin but Yahwi “wins” in the end and is actually with Jooin. Cain will ultimately “lose” and not be with Jooin so why does his life still revolve around him like some pathetic abandoned puppy? Moving on is doing what Jooin did and forgetting about him. Period.