Sweetie Belle has grown from a filly to an adult, growing up with her BBF's the Cutie Mark Crusaders. Somethings don't ever change like Twilight and the mane six remaining as friends and her sisters constant help in friendship matters.
What has changed is that She, Apple Bloom, and Scootaloo help sometimes with friendship problems, Spike is no longer a baby dragon now taller then Twilight. Twilight is getting married, Rainbow dash and Fluttershy are in a relationship, Apple Bloom and Scootaloo are also in a relationship, and Spike still loves Rarity.
But that changes on the night of Twilight's wedding when yet again Spike gets shot down by Rarity and this time it seams to be the last time as Spike now seams totally defeated once and for all, Sweetie Belle feeling bad for her dragon friend goes to comfort him but discovers that she has more then just a feeling of concerned for her friend, she just never realized it was more until that day.
But now how will she confront these feelings after all he had loved her older sister for so long will he just use her as a means to an end or will he see her as herself, getting help form unlikely ponies and her friends she'll try to pursue this now blooming love.