Her Wager With The Duke: Amazon Link

The widowed Eliza, or Lady Lytton, has spent the last years relishing in her freedom and extravagant London lifestyle. And despite her refusal to let any man approach her, she finds herself caught up in an illicit wager with the worst of them.
The Duke of Wordsworth, Timothy Hansen, is a rake and proud libertine. But after his latest mistress unfavorably criticizes his skills in the bedroom, he is looking for reassurance. And his widowed friend is the only one to be trusted with it.
With her undesirable brother-in-law asking for her hand in marriage though, Eliza is afraid that her carefree days are over. Only, it seems that there is more at stake than her freedom. For she and Timothy both stand to lose not only the wager they have placed but their very own hearts…