A year ago, Applejack came to Rainbow Dash about her conflicting feelings for both her and Rarity. Since then, she has chosen Rarity and they've been together ever since. When Applejack has something to confess to Rainbow before Hearth's Warming, she panics because of how much she can tell that AJ and Rarity are perfect for each other, and worries that she'd pale in comparison. Especially when she realizes they aren't even going to break up. Nope. She and Rarity want to start a throuple with her.