A matter of choice - Nora Roberts

Sgt. James "Slade" Sladerman had practically been born to the force, but he wanted to be a writer, not a cop. No one was more different from him than Jessica Winslow, who was wealthy and working only because she wanted to.
He felt the gap between them keenly, and almost refused to be her undercover bodyguard. But someone had to watch her and he'd given his word-regardless of her innocence or guilt.
Slade couldn't afford to care, but built into the shadow of danger, in the arms of the woman, he'd sworn to protect, Slade knew whatever the price, he'd meet it.