I have read 'for your love' (the author's previous work), and in that you can see that Yuri is a smart kid with good grades. Not only that, he was quite an observant person. He was the first one to notice Yohan (his bestfriend and mc in FYL) developing feeling towards hyung and was one of the people who helped for their relationship to happen. He is still an observant person, considering he understood that Jiri is in depression and also realized that Jiri's was a pure love..... #-.-)
I belive if Yuri was not in that situation (I mean if it was not his noona who married Jiri's love) and had met his teacher and saw him getting depressed like this, he would have surely helped him to get through it, atleast a little......(since they were good friends back in his HL days)
BBBBUUUUUUTTTTT no!! the whole situation itself is messed up and Yuri just dont want to use his BRAINNN!!!!! ( ̄へ ̄)He is acting like a spoilt kid and taking out his anger in the meanest way possible!!!! and our poor Jiri is becoming its victim ╥﹏╥ (he was always mean to begin with...but this 'mean' is in a whole different level!!)
If you see the expression Yuri made when Jiri said "now that you have insulted me like this, do you feel better?", you can see that Yuri knows that he did wrong and STTIILLLLL he do not want to APOLOGIZE like a normal person....because all that Yuri can think now is HE and HIS FAILED LOVE!!!! (/TДT)/
I am daaaammmmn sure that when Yuri will get back his brain and get over this failed love he is gonna regret soooo much!!!1 aaaahhh this is killing meeee..