yes you are missing something!
(spoilers)
the fallout happened when they were well into college. Minyoung (pale guy) told Cheol (tan guy)'s dad that he's gay. The dad is homophobic and physically abuse. It was totally overstepping Cheol's boundaries.
More context if you want:
In other chapters, when Cheol was a little out of his mind and didn't remember anything after the fallout, he says that no matter what Minyoung did he would forgive him if he sincerely apologized and Minyoung admits he never apologized.
And in a more recent chapter (again don't remember which one), Minyoung says back in college he wasn't "strong" enough to protect Cheol. So, I think that's why he didn't apologize right away and waited 10 years. That's what I understand so far but if what I said doesn't make sense to you or you don't remember I would suggest rereading from the beginning because it's well written!
This is only spoilers until the latest chapter 33! I don't read the novel or raws btw!!!
so when did the fall out happened? I thought it was at HS graduation but they still in contact after graduation? Am i missing sth?