It’s Always the Duke by Lisa Campell

Having a man as your best friend is great. Until you fall for him…
Miss Caroline Wentworth refuses to attend any Season in London. Her heart belongs to her childhood sweetheart. And even if he stopped loving her, she prefers to stay a spinster than marry another.

Then, a suitor appears. Someone she cannot decline. For her father owes him, and she is the debt’s payment.
Edward Brandon the Duke of Darkwood has just returned to London scarred from the war. He enjoys waking next to different women every day, doing anything to forget the battlefield’s horrors. Oh, and he is sworn to stay unwed forever. After facing Caroline again, Edward is determined to keep her away. As soul-crushing as it is, he knows that he cannot give her what she deserves, even if his heart aches for her.

But when circumstances force them to live under the same roof, the atmosphere is electrifying. Caroline must wake up Edward’s feelings before she is forced to marry, while the devilish Duke must guard his heartbreaking secrets.