His Temporary Duchess by Claire Devon

“I ought to punish you,” he murmured, kissing her, “for tormenting me in this way.”

Lady Eleanor has spent a lifetime in the shadows, overlooked and forgotten. But when the Duke offers her his hand over her half-sisters, she is determined to turn their marriage into something real…
Duke Sebastian needs a wife—one he can easily cast aside. His plan is simple: push her to the brink until she begs for an annulment. And who better than the demure, forgettable Lady Eleanor?
But from the moment their vows are spoken, it becomes strikingly clear—Eleanor is anything but meek. The more he pushes, the more she defies him, and soon, resisting her becomes nigh on impossible…

Each book in the Dukes Ever After series is a standalone story of 70,000 words that can be enjoyed out of order and can be read for free with Kindle Unlimited.