
Well, you see the author is pretty clever os the ending so far can be left for interpretation in case they don't manage to finish it.
It's withe t
A) he died, the end
Or
B) He lost all the fight in him and refused to eat, thus he passed out from a lack of water. He just needs some h20 and he will be hella fine. (what I think is the case, plus this would make more sense)

He's dead.
Mentally and emotionally dead, I mean.
They made a promise in the beginning of the few chapters, if dohyun remembers their past, sungho would release him. But even when he already remembered, Sungho still intend to keep him. He even tried to touch dohyun against his will again.
After he went out of the room, that's when Dohyun recall back that he once found a dog, but the dog died. Life is fickle, the real owner of the dog doesn't even know if their dog was still alive or not.
And he thinks it's the same in his case.
if sungho keep him alive, life's still gonna be tough out there.
So simply put. he's mentally exhausted and have had enough.
I never seen anything like this before. It has everything I need and want to see in it. I love how empty it makes me feel. I hope this continues soon or else I isn't know what I will do.