Sometimes I think that Severus is not a master spy but master of misunderstanding. I know that it could be because of his insecurity, but sometimes it is just... stupid. I'm pretty sure that Harry was just so happy that finally he is with Severus that he had to floo Ron and Hermione.
Sweetheart is a very good word to describe Severus :) I think that he likes it, but hush! You don't know it from me.
Hugs,
myk