My one and only...or not // Niall Horan fanfiction

Katelin Summers and Calista Dallas have been best friend's sins childhood, but they separate at 17, when Katelin moved to Doncaster.
They still messaged and skyped and even met up a few days on the holidays, but after a year they slowly drifted apart. Until they got to collage, and found out, they we're roommates, and became close again...
But there was a catch, they had to share a room, they had to share a room, with 2 girls...or should I say boys.
The on isn't a problem, his Calista's older brother, Cameron Dallas, Katelin always had a small crush on him, he was very hot, but sweet at the same time.
But the older guy, Niall Horan, was a small problem. He was cocky, arrogant, hot frat boy. He had a reputation of sleeping with girls, having one night stands, and breaking girls' hearts.
What happens when Katelin, the straight A-student who absolutely hates partying and Niall Horan, the frat boy, have to share a room...