Harry Potter and the Half-Blood Prince
House: Gryffindor, 4th Year
Romilda has a HUGE crush on Harry Potter, the likes of which compel her to give him some chocolates that are infused with a love potion (procured at Fred and George Weasley's joke shop). Fortunately, Harry doesn't eat the chocolates. However, Ron does (many months later), and he instantly falls in love with Romilda Vane. His crush is so intense that Harry takes him to see Slughorn in the hopes of securing an antidote for his friend. While at Slughorn's office, Ron falls deathly ill after sipping a poisoned drink.