I've serious doubts about the stairs... Grayson did it ...he is the one

Yea, he is a sociopath, probably even psychotic. Lack of human compassion, empathy, or even remorse.

But he learns the emotions from Dane . And changes himself for Dane

no he didn't, novel did not mention about it. The building was seriously destroyed and on the verge of collapsing. The manhwa did not show how severe it was so I'm disappointed. Dane's life was really in danger.