I wouldn't say "he got what was coming to him", not even he deserved that. I also wouldn't say he "realized his atrocities" either. He never showed any remorse, i don't think he cares about anything anymore, he only ever cared for his mother. I think there was a CHANCE, a very small chance, that he would've eventually fallen in love with Sihyoon as it shows him sympathize with Sihyoon a few times, but all that died the moment his mother died and he died inside. I don't think he feels bad towards Sihyoon OR Junsik so much as that they don't matter to him anymore. He tried to kill himself already as shown by his cuts and he's planning to either kill himself and Sihyoon or to arrange a double suicide with Sihyoon.
In the end,the uke got what was coming for him.His past selfish,manipulative and cunning choices came to bite him in the ass and only after losing the only important person in his life did he realise the atrocities he had commited.A classic,twisted and unfortunate example of karma performing it's magic.