
"He kept muttering Kim Dokja Kim Dokja" lol bro no one can defend you any longer at this point. He's going crazy with the departure of his beloved husband.
Spoiler below
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He's actually trying to communicate with Kim Dokja via their telepathic personal chat box. He'll be coming soon to the 73rd demon realm with Uriel's help, and YJH will identify himself as KDJ, just like how KDJ did him dirty.

Can someone provide me the spoiler on the ending of this manhwa?

damn, this ending would have been truly horrifying.
But no, the ending of this story is actually the typical happy ever after ending. They get married and had a baby, although it was not specific whether the baby is a boy or girl. But before that happened, ML did do horrible things to the FL. Like, seriously. If it happened to me, I would've preferred to die. But what the OGVillainess did to ML was vile too , so ML's behaviour towards the Lyna now is understandable. But man, you should all brace yourselves for when the ML locks the FL up in that cottage he had made specifically for her.

Is not it that (⊙…⊙ )the professor is into blondie and blondie is into redhead and redhead is into professor and the professor knows it so he is using it to his advantage?

I don't think the prof holds romantic feelings for the ml. In the first chapters when ml answered wooju's call in the presence of cha, the latter didn't have any kind of reaction. I think it's more connected with his mother actually or something like that.
Plus, from the cover the professor's hand touches mc's cheek, so I think at last he will develop romantic feelings towards him. But then, he who knows
Their "call me by your name" phase going in full swing (≧∀≦)