Rarity is shown to be very fond of Spike especially in the episodes "A Dog and Pony Show", and "Secret of my Excess" and "Dragon's Quest".

Who does Rarity end up with?

Moonverse. In SPF's main Universe, Rarity meets Crystal Varado while vacationing in the Cystal Empire. The two strike up a conversation and decide to keep in touch. Several years later, they end up marrying and having a child, Dusk Lazuli.

Who does Spike have a crush on in my little pony?

Spike develops a crush on Rarity the moment he sees her in Friendship is Magic, part 1, a scene that was written by Lauren Faust to illustrate Rarity's beauty to the audience. He goes to great lengths for her affection.