Faking It by Diane Alberts:
Derek Rory never meant to propose to his best friend's little sister. But when her boss tells a family-oriented investor he's Stephanie's fiancé, Derek can either play along or let her get fired. He's hardly one to turn away from a damsel in distress. If only that damsel wasn't adorable and sexy with a laugh that could melt any cold business mogul's heart.
When a business proposal becomes a marriage proposal, Stephanie Miller tries to keep it strictly boardroom. But when things get hot under the table, it's all they can do to stay apart. As the tangle of lies drags them deeper into the underhanded world of business politics, Stephanie finds herself in over her head—not just with her job, but with her "fiancé." His eyes are cold, but his kisses light her on fire. If she's not careful, she'll end up faking her way into a real romance.