Losing Control (A Babysitting a Billionaire Novel) by Nina Croft

Four years after escaping her abusive ex-husband, Kim finally believes she's in control of her life and her emotions and she's determined to never risk either again with a man. She has a great home, a job as a security specialist which she loves, and Jake for a best friend. But things are a tad lonely in the sex department, so she decides to embark on a no-strings-affair with one of her hot co-workers. And who better to help her remember how to lure a man than her best friend?

Jake has wanted Kim from the moment he first saw her, but four years ago, she was too young and too damaged. So he kept her close and he kept her safe, offering her a job in his security company and the training to feel safe again, and he bided his time. But now, after the long wait, if she imagines he's going to stand by while she seduces some other guy… Never going to happen.