My Perfect Enemy by Jessica Prince

Rule number 1: Never fall for the enemy.
Rule number 2: Never get involved with a local.
Luna Copeland lives by those rules, which complicates things tremendously when her new boss turns out to be a former one-night stand. As if that isn’t bad enough, he’s also a world-class jerk. But she just can’t make herself stop thinking about their one night together.
When Nate Warren left Whitecap years ago, he was certain he wouldn’t come back. But when his daughter starts acting up and getting into trouble, the small coastal town proves to be the best place for her. With an unruly teen on his hands, the last thing he has time for is romance. Unfortunately, he can’t get his sassy assistant out of his head.
When ignoring their attraction fails, Nate decides he wants all in. He just has to convince Luna she wants the same.