In Harry Potter and the Half-Blood Prince, when Potter isn't whisking through space on Dumbledore's arm (this is really a father-son fromance) or dipping his face into other people's creepy memories, he and pals Ron and Hermione are entangled in various teen love intrigues--one even involves a powerful love potion. Movieline goes to the source (Daniel Radcliffe and Emma Watson) to get the skinny on who hearts who.