I think more than getting off on it he's just enabling him because he's afraid of losing him again, but I still thought (or hoped) they'd move on from all that dad/son thing but clearly Nanmu is waaay too attached to the idea of having a family that he'll do anything and accept it even if it makes no sense like this. Though Pilgyun seems OK with it and would rather be lovers.

I feel so weirded out woth the dad thing, their relationship is so complex, they depend on each other alot especially as the nonsense family they are, but to me it's still feels like "how can they still be acting as if their relationship is of a father and son?!" , I'm waiting to find out they'll go on from here on but I was really surprised when Nanmu was so mad that Pilgyun didn't want to be his son anymore, I thought after having sex he'd be reluctant to keep wanting him to call him dad and I also felt it was way too easy for them to jump into sexual relationship, hoped they'd take longer but I guess they're both not normal.