Imma need some chapters from Nanjo's perspective cause I got no idea what he's thinking.

I think he was already enjoying his time with Mok-yeon. After reading the author’s note and reading season 1, by the time the final threesome had come around he had started to soften to him. I think he does have a savior complex, so seeing Mok-yeon so pathetic may have triggered it enough for him to give in again.