"You remember, a while back. When... nevermind." No need to bring up the whole potion part, not relevant. "When you were bein real honest about shit? Well, I been thinkin about it. You're more'n my best friend. And I shoulda said somethin' sooner. I like spending time around you. And... I like you." He says it quietly, a little bit worried that he might have waited too long to actually say anything. Or that Harry might think he was only saying it because he was lonely and missing Caleb.