This story is a sequel to Sparkle Kitten
Twilight Sparkle and Rarity are about as happy as two ponies can be together. Their love is about to be tested, though, when Twilight's former flame returns to Ponyville to take back what was once hers.
This story takes place in the same timeline as Sparkle Kitten and Trixie's Great and Powerful Revenge. It's written without taking the events of Magic Duel into consideration, as I thought of this idea a good long while ago, but only just got to it.