I could not remember what happened in the past. Why he hates Jihwan?

I lowkey forgot too. Something to do with overhearing his phone call to somebody? I think? Something to do with basically his life being toyed around with? I think!

Well he found out that jihwan asked school authorities to manipulate his result and as things keep unfolding in the past he also found out that jihwan tricked and isolated him

Thank you<3