My thoughts are that the MC died in a previous life and the dark haired seme is probably related to the death somehow or contributed in some way annnnd light haired seme also has a crush on him and probably kissed (or some explicit stuff) the MC after he died (maybe at funeral or right at time of death).
Idk, that’s my speculation. Haven’t read anything or seen any races.
If you don't mind a spoiler
So the light haired guy has a crush on Yesung (both him and the ML's math tutor) which somehow looks exactly like our MC. He was ill and couldn't stand living anymore so he told our ML to turn off the breathing medical machine (?) so he could die in peace. That's why the light haired dude kept telling the ML is a murderer while ML told the light haired guy necrophiliac because he kept obsessed over the dead tutor and even reflect that obsession on our MC just because they look alike

Why is no one talking abt the light haired guys necrophiliac allegation??? I NEED to know what happened in the past with both ML's bc wdym "Murderer" and "necrophiliac"!! Like did the light haired guy actually fuck a dead body?? I NEED ANSWERS ToT