Spoiler: S9 E19, Seriously this time
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I really enjoyed this episode, if my previous post didn't make that already clear.
As the final that really touches on "Sparity", this is more or less how I pictured the show to deal with it if they didn't want to actually sink the ship. The show was never going to be able to get away with flat out making them a couple onscreen, so the next best thing was to showcase how Rarity has come to feel about Spike, and having that be through jealously at having to compete with somepony else for Spike's time works perfectly with Rarity's character. One of Rarity's single biggest flaws has always been, ironically enough, the fact that she has a major greedy streak, so having her be possessive of her Spikey-Wikey fits perfectly with that. But, beyond simple jealously, the episode shows how close the two have become and how Rarity has come to rely on Spike in many ways, not just as an assistant but as a companion.
Also, interestingly in this episode Rarity learns a lesson we've seen before with another character in a ship this season seems to be pushing, namely Discord learning the need to share Fluttershy. Coincidence?

Overall, this is another A episode for me.