I totally agree, this just felt so unnecessary and honestly so childish.
Yeah, that would be the case normally. But, Jinwoo's words the day before were already triggering him so much he ran away and didn't even bothered reading the letter or checking out the gift Jinwoo left to him. Then Jinwoo just moved out without giving an explaination so it must have triggered him even more. He was already thinking Jinwoo was gonna dump him but after the talk he had with his friend he made up his mind to not let go. May be seeing Jinwoo move out without giving him an explaination must have just drove it home in his head that Jinwoo wanted to dump him but slowly. And now his preservation instinct is like, I'd dump him before he can dump me.
That doesn’t even sound like something Daehan would say. Bro would neeeever break up with Jinwoo like that. I get we need drama but that just feels way too unbelievable from his character. He was JUST crying about not wanting to break up with him in the previous chapter.