What is the name of the song Taylor wrote for Joe Jonas?

Today is Christmas day! I'm soooo happy :)
Merry Christmas Swifties! :)
Now, If you got the correct answer. I am going to make a cover for your book, just only one book. If you doesn't have a book I am going to follow you. This is valid until December 31, 2015.

P.S. I am going to send the cover through Kik. My Kik name: BlinkOfAnEye13

-Vote and Comment your answers Swifties!