Tweaked from Spark Notes.
The next day in Potions, the students are assigned antidotes, and the Half-Blood Prince’s textbook is of no help to Harry.Apparently the Half-Blood Prince understands Golpalott's Third Law very well whereas Harry isn't grasping it at all and Hermione can't hide her glee over it. He finally finds the words “Just shove a bezoar down their throats” scribbled in a margin. Rummaging through the supply cupboard, Harry finds a bezoar, a stone from the stomach of a goat, and runs back to his seat. When Slughorn approaches his cauldron, Harry hands over the bezoar, and Slughorn laughs and awards Gryffindor with points, making Hermione quite livid.
After class, Harry hopes to cash in on Slughorn's joviality and asks him about Horcruxes, and Slughorn freezes. He knows immediately that Dumbledore has sent Harry and refuses to answer. The students begin their Apparition lessons. It is normally impossible to Apparate or Disapparate within Hogwarts, but the restrictions are lifted within the Great Hall for one hour so the students can practice. The lesson however doesn't go well for the students, none of them manages to Apparate. Harry uses the opportunity to spy on Draco Malfoy and learns that Draco hasn't finished something he's working on and Crabbe and Goyle are obviously fed up with being on the lookout for Draco all the time. After Apparition practice, Ron and Harry return to the dorms, and Harry pulls out the Marauder’s Map to try and locate where in Hogwarts Draco is. Ron spots him in the Slytherin common room. Harry continues to regularly consult the Marauder’s Map to check on Draco’s whereabouts. Sometimes he is unable to locate him on the map at all.
On the morning of his birthday, Ron tears through the presents at the foot of his bed as Harry rummages through his trunk for the Marauder’s Map. Ron starts eating Chocolate Cauldrons and leans on his bedpost, looking unfocused. Ron tells Harry he’s in love with Romilda Vane. Harry suddenly realizes that Ron has eaten the love potion-spiked Chocolate Cauldrons Romilda slipped him before Christmas - they fell out of Harry’s trunk and Ron assumed they were one of his presents. Acting quickly, after Ron had punched him for supposedly insulting Romilda, Harry decided that the best course of action is to bring Ron to Slughorn. On the way, they run into Lavender who becomes angered when Ron dismisses her completely. They finally make their way to Slughorn's quarters. After hearing about Ron's dilemma, Slughorn makes an antidote, which Ron quickly drinks. Slughorn pulls out a bottle of oak-matured mead he intended to give Dumbledore for Christmas and pours Ron a glass. Ron drinks his before the toast is over and suddenly shoots up in the air, his eyes bulging and foam coming from his mouth. Slughorn appears mystified, and Harry sprints to the cabinet and finds a bezoar, which he shoves down Ron’s throat. Ron gasps and goes still.