Responses
Because Hosik can be easily manipulated. To this day he can not accept what he did to Hosik if he wasnt pregnant I'm pretty sure he would of beaten the crap out of him by now
It's more of FOR Hosik, they need to fight every once in awhile so that Sunbae wont be so controlling. This was actually all explained a few chapters ago when Hosik went to Jiwoon's house. Is he being petty about it while trying to help Hosik? Yes. Because the reality is that Sunbae is creepy and he has never really liked him, but at the core, his actions are for Hosik.
Why does Jiwoon keep provoking Sungyeon and causing the two of them to fight? I get that he doesn't like him, but he should at least care about Hosik enough to not be so petty all the time.