Fire in my Heart (Niall Horan)

Alicia Styles never meant to be in love with Niall Horan.
Niall Horan is the typical.. not typical.. he's the hottie in the group.
Everyone likes him.
Niall casually fell for Alicia, just as Alicia fell for him. Perfect love story, right? WRONG.
I didn't tell you the details of Niall Horan. Let me tell you, Niall Horan is the guy who's decent and clean. Perfect for a boyfriend- during the day. At night, he's a wild animal who hooks up with girls at the bar. He takes off his long sleeved to reveal tattoos. He puts his piercings back in. Like I said, he's an animal.
Alicia Styles is the typical girl. Cute, funny, sweet, beautiful.. and clueless. She is the nerd. Never gets drunk. Stays clean. You wouldn't even notice she's there.
What happens when she finds out about Niall?
What happens when she breaks up with him?
Niall said he'd be back for her...
What does this mean?