Good Duke Gone Rogue by Eliana Piers

Lady Bernadette is almost desperate. Almost. As a widow from a marriage of convenience, she does not want to go through that torment again. But she will for her son. She just wants a little bit of time to discover herself, to breathe, and to prepare for a loveless future.

A bit of a rogue, Lord Reggie does and says whatever he wants, whenever he wants. In line to be an earl, he knows he needs to grow up, but he has time. Until he doesn’t. When an old friend shows up at his door, secrets from his past can no longer stay hidden, and an unquellable fire begins to burn.
But does falling in love with your friend make a good match?