The Fighter's Girl by Jenika Snow
Izzy Castle's life is anything but exciting. Her only entertainment is working at an adult store, but even that leaves a lot to be desired. But when her roommate of only six months, Brock Larson, makes a move on her, Izzy decides that a little harmless sex with the cage fighter might be just what she needs to feel alive. But she has seen his other one-night stands do the walk of shame, and Izzy doesn't know if her heart can withstand that humiliation.
Brock fights for the underground circuit. He takes what he wants, when he wants it, and makes no apologies for it. He wants Izzy, but it isn't for just one night—what he's used to. Izzy's his, and he will get his knuckles bloody proving that he may be roughened, but when he wants something as badly as he wants her, he won't give up.