Wondered about this too...but like we can see how much he cares about Gyeong Joon (aka that whole ass “confession” the last chapter about not leaving him). So I’m cool with a long wait for his calling him by his name, cause readers at least know that Cain doesn’t consider him as just a human.
To the people who reads the raws: will there be a time when Cain won't call Do Gyeong Joon human but by his name?