My Brother's Best Friend - An R5 FanFiction

Allison and Erin are twins, best friends, inseparable, until their parents get a divorce. Erin lives with their dad and moves to California while Allison lives with mom and stays in Connecticut. The twins see each other only for their birthday and Christmas, most of the time at Erin and their dad's place. Ali loves it there, so as soon as they graduate her and her brother get an apartment together. But there seems to be an unexpected guest hanging out there, Erin's best friend, Rocky Lynch. Him and Ali hit it off, they become best friends as well. Erin warns her to stay friends with him, "he's a bad boy. Plus, you have a boyfriend." But after Allison breaks up with Scott, she finds herself in bed with her brother's best friend.