Oh you gonna love him in the future
Trust me when I say he's gonna grow on you in the future. And, yes, he has his own reasons for not being friendly with others, but which will be explained in the later chapters.
PATIENCE IS KEYYYYYYY just remember it's only chapter 70 out of 600-ish novel chapters.... there will be character development for everyone involved, i assure you.
YOU GOTTA WAIT TRUSTTT
Guys I'm gonna be roasted for this but I dont care for little Sejin.
In the show we see how hard he was working to debut and be an idol but somehow he doesn't even try to be friendly with the others, and it's like those situations that being in a group doesn't work for him.
Ig his way of behaving is gonna be explained in the upcoming chapters but I cannot pretend that I love him as much as the others