Song:

You Belong With Me by Taylor Swift

I don't really want to spoil the plot, but basically Kaylin's loved Enjolras ever since she met him on the first day of school. In the winter, he starts dating a girl named Terrie Marie, who seems to not understand what a dress code is, hence the 'she wears short skirts' part.

Later, Enjy and Tari Mari (Les Amis' nickname for her) break up and Kaylin and Enjolras start dating. I'm planning for this song to come up in the book, so stay tuned!!

She's going off about something that you said
'Cause she doesn't get your humor like I do

But she wears short skirts
I wear T-shirts
She's Cheer Captain, and I'm on the bleachers
Dreaming about the day when you wake up and find
That what you're looking for has been here the whole time

If you could see that I'm the one
Who understands you
Been here all along
So, why can't you see?
You belong with me
You belong with me

And I know your favorite songs
And you tell me 'bout your dreams
Think I know where you belong
Think I know it's with me