Comment by Jaeshins_Third_Leg on Eighteen's Bed - Chapter 65

This is the catalyst to the whole reason you've seen scars on Yohan's back in the future college special episode...
Up until the last minute, Kang Jun is ready to betray Yohan since he's really upset with him. But he suddenly changes his mind - because deep down he loves Yohan and also he sees Yohan as someone that can help him survive more so than Minho (bully) who is a moron. 

Ultimately Kang Jun tells Yohan what's up, while Minho about to film Yohan confession or so he thinks 💀 and then Yohan pretty much beats his äss but this is just the beginning of their troubles because this sets the villain arc for Minho.
He becomes obsessed with getting revenge on Kang Jun.
So in their college days, he will do something unspeakable and it will be meant to hurt Kang Jun but Yohan will end up taking the hit.

However, this is what allows their relationship to really begin. Things heat up quickly and they have lots of wild sëx and fluff and everything. They even talk out a bunch of their issues and over the years it becomes way less toxic.  Basically, without this event, they would have never gotten together. You'll see that later as well. 
So we can call the Minho bully character a twisted Cupid, if you will.
This is so peak, but the climb is daunting.