He - doesn't actually know how to respond to that. Usually the proper thing to do in this sort of situation is say 'I love you, too' except, he actually doesn't. He likes her, certainly. But love? No, he's been in love before, this is not it. He's pretty sure that anything he could say would just sort of - make everything terrible. Because his conversation skills are sort of lacking, after a long time of misanthropy. 'I don't quietly hate you' is probably not the best response, either.

So, he doesn't say anything, and just snuggles her a little closer and kisses her hair.