Cruel Surrender by Terri Anne Browning

Bain: Destroy the Vitucci family from the inside out. Break them as they had broken our great-grandmother.
That was the plan.
Then I set eyes on Ciana Donati.
The moment she appeared before me, everything changed.
Sheena might think that I was her loyal soldier, but I was the one she should fear.

Ciana: All I wanted was a little time away from the craziness that was my life as a Vitucci princess. I promised to be on my best behavior if they would just let me go on vacation—and I meant to keep that promise.
Then I saw the sexy stranger on his balcony next door, and my entire world shifted.
I didn’t plan to fall for him, but as we shared bottles of wine and our darkest secrets under the stars each night, I gave him my heart.
Never once imagining it was all part of his plan to use me to hurt the person I loved most.
Heartbroken, I returned home, determined to forget the biggest mistake of my life.
But I brought a lot more with me than just a shattered heart.