Rainbooms and Marshmallows by electreXcessive
Link - http://www.fimfiction.net/story/136658/1/rainbooms-and-marshmallows/a-day-to-remember

"Rarity is depressed. She's been used and hurt before, but when one too many stallions abuse her, she gets pushed over the edge. Shutting herself away from civilization, it's up to a familiar rainbow maned pegasus to cheer her up."

Music used - This Kiss (1998) by Faith Hill
I own nothing in this video.