Chapter 15 - "The Unbreakable Vow" - In which Hermione stays angry with Ron but Harry tries to stay friends with both, Harry finds that girls are trying to seduce him, and Romilda Vane tries to slip him a Love Potion. Harry then asks Luna to Slughorn's Christmas party, and Hermione invites McLaggen to upset Ron. After some general mingling at the party, Malfoy is caught prowling the corridors and Snape takes him away to an empty classroom, where Harry overhears Snape's offers to help Malfoy and Draco's refusals.
Ron Feels Inadequate
As [Harry] and [Ron] return from a lousy [Quidditch] practice, they run into [Ginny] and [Dean], kissing in a hidden passage. [Ron] yells at [Ginny] but [Ginny] embarasses him and walks off - leaving behind an angry [Ron] and a [Harry] who, for the first time, realizes he's attracted to her.
[Harry] and [Ron] walk back to [Gryffindor Tower], Ron furious at [Ginny] and [Harry] confused over his feelings for her. Harry then all but admits he thinks [Hermione] snogged [Viktor Krum], and he and [Ron] both go up to bed, deep in thought.
Angry that [Hermione] snogged [Viktor Krum], [Ron] becomes moody and agressive, his [Quidditch] skills fall apart, and the night before the [Gryffindor]-[Slytherin] match, [Harry] tries unsuccessfully to spur his confidence.
Ron Feels Lucky
At breakfast prior to the [Quidditch] match, [Harry] pretends to slip [Felix Felicis] into [Ron]'s [pumpkin juice], making [Hermione] angry.
While getting ready for the match, [Ron] realizes that [Harry] slipped him [Felix Felicis] - boosting his confidence as the match is about to begin.
The [Gryffindor]-[Slytherin] Quidditch match. [Draco Malfoy] skips the match, [Zacharias Smith] commentates, and [Gryffindor] wins when [Harry] catches the [Snitch] right in front of [Harper], and [Ginny] celebrates by crashing into [Smith].
In the [locker room] following the [Quidditch] match, [Hermione] confronts [Harry] about slipping [Ron] [Felix Felicis] and [Harry] admits that he faked it - and both [Ron] and [Hermione] leave upset with each other.
"Hell Hath No Fury..."
At the party in the [Gryffindor common room], [Harry] can't find [Hermione] but [Ginny] points out [Ron] snogging [Lavender Brown]. [Harry] then leaves, sidestepping [Romilda Vane], to find [Hermione].
[Harry] finds [Hermione] in an unlocked classroom, sobbing. Before long [Ron] walks in with [Lavender] and [Hermione] makes her birds attack him and runs out.