But yeah, in summary it all started when Apple Bloom started visiting Zecora, interested in the potions she taught her to make potions.
Years passed, and Apple Bloom began to grow and mature. At some point, she fell in love with her "potions tutor" and she kept it a secret for many more years, until of course she can't keep it only for her anymore… but she was scared… she didn't know how her family and friends gonna react to her crush..
Then… one day she decided that she can't keep it anymore, and Apple Bloom told Zecora how she was feeling…
Thinking she was rejected, she ran off of Zecora's home and she when to her own home in a stormy night. Apple Bloom told everything that happen to Granny Smith and her siblings.
And then, after a few moments, Zecora appeared in the barn where the Apple family was. To the surprise of Apple Bloom, the zebra corresponded her feelings … after all those years, how could she not have feelings for her?
The next day all Ponyville learned about the new couple, so Pinkie Pie gave them a party at Sweet Apple Acres, and all the friends and family came.