Let's give him some slack, he's a literal child while the MC is an adult in a child's body. Considering that Namgung grew up to be a fine man and treated MC well despite her avoidance and utterly disgust about his behavior, I'd say I wouldn't care about these two children's chemistry when they're too young to pursue a romantic relationship at the moment. There will be immaturity in their relationship cause again, they're children, especially Namgung.
I SHOULDN'T HAVE READ THE COMMENTS I GOT SPOILED WTF DO YOU MEAN YAYUL IS NOT THE ML BE FUCKING REALISTIC AUTHOR BE BETTER PULL A MOVE OR I WOULD DROP TJIS SHIT