There's a very interesting theory by tastytoast below in the comments. They said it could be a case of fate exchange, nam woori's family mightve done something to exchange fate and fortune of soobin with woori so that he can live a good life. Maybe woori was born with bad fate and his family decided to give all that to the innocent soobin and take his happiness and luck and give to woori. Soobin could've come to know abt it and killed mc each time to take the stolen luck back. I also find this theory very plausable coz we see soobin again and again mention how his life is in ruins specifically becoz of woori. Op also mentioned how we see woori's grandma asking woori to always keep that ring with him, maybe that is the source of it all.
woah that seems really plausible they might have just gone and guessed the whole plot! does explain a lot of soobins behaviour.. well i do love morally gray characters regardless and having all your luck robbed from you would break me too ngl
nothing i’ve seen has justified soobin murdering him all those times??? like sure he’s rich and ignorant but that is no excuse