The Duke's Wife (The Three Mrs #3)
Jess Michaels

No one can push Gilmore’s buttons more than the fascinating Abigail Montgomery. They constantly butt heads and yet he can’t get her off his mind. But now that her year of mourning for the husband who betrayed them all is over, she is showing up in his life a lot more. When a series of playful wagers leads to a passionate moment, everything changes.
Now forced to marry after being caught together, the two must navigate a tangled past and a cloudy future. Could these enemies ever be more than lovers? Or will their stubborn hesitation to get closer keep them from being truly happy together?