Based on Delirium by Lauren Oliver.

A thousand years ago, the world was almost lost due to love - the deliria - when it turned sister on sister and brought Equestria to its knees.
Now things are different. Now scientists have been able to eradicate love, in a procedure each pony must undergo when they receive their cutie marks.
Applejack has always looked forward to the cure, to living a life free of love and, with it, from pain.

But as her treatment date draws near, she does the unthinkable:

She falls in love.