The pink hair guy was going to kill mogum(I dont remember too much his name) only because he won the paper of the movie when they were little, that's so childish
No he wanted him dead because of his crazy obsessive love for Doyoon. He saw him as "stealing his man" pretty much. The step father praising Moygum was just like the finally straw that caused him to snap.
So he is dating the both of them wth In my opinion he should stay with the big brother I didn't mean to read a threesome I thought it was going to be only a couple
Espectacular