[He does feel something different, and even if he doesn't get her exact message the meaning reads clearly. It is kinda scary, and he's not sure he's ready for this but at the same time... when are you ever? Is there actually a point where you can say yes, I'm ready for this scary thing?
Probably not, and so he just lets it be as scary as it wants to be. He pushes back into the kiss a little, to show that he got it. That he probably would say something similar.]