Down and Dirty (A Dare Me Novel) by Christine Bell:
He was a dare she’d never been able to resist…
Cat Thomas has never been the kind of girl to stick. A self-professed infatuation junky, she latches on the newest, hottest guy on the block, then finds a reason—real or imagined—to dump him. When she accepts a dare to rekindle her high school flame and jump in bed with her brother’s best friend, Shane Decker, she knows she’s in trouble. She can’t resist the man, even after all these years apart, and that just won’t do.
Shane has come back to town for a couple reasons. The biggest one? He’s tired of living away from those he loves, including Cat. But now she’s spooked and will do anything to drive a wedge between them, including trying to fix him up with other women through an online dating service.
What does he have to do to make her see that settling down doesn’t mean settling, and he’s ready to spend a lifetime proving it?