Harry seems so disappointed that Severus can't think of one thing he likes. *Pouty* of course like doesn't necessarily mean anything when relating to love. Millicent and her questionnaire don't know a thing about love either :p

I'm sure if Severus tried he'd be able to think of something- how Harry calls out his name, or the look on his face when he's concentrating really hard. Something silly, but super romantic. - and he just didn't want to say it because it's super embarrassing.