He just had to be sure before doing anything drastic like confronting the culprit; he had to test his theory, but he had no idea how. He knew next to nothing about love potions, apart from what he learned during Potions class, and they hadn’t really practised making an antidote for them. Such a thing must have been in existence, though; maybe he could ask Slughorn or just look for the answer in the library, Hermione-style. 