Besting the Earl by Allie Kensington

Two matchmakers, with a scheme to help their friends form an attachment, find they are entangled in an attachment of their own.
Mary’s task was supposed to be an easy one. During the London Season, she pretended to be smitten with the Earl of Dorset in order to give her cousin the opportunity to make a smart match. The plan was a successful one, but pretending to be in love with Lord Dorset affected her heart. When he doesn’t return her feelings, she’s resolved to settle into life without any more pretending.
When Lord Abingdon comes to town he turns everyone’s head. Mary is intrigued by the man before her—finally someone real, whose regard for her isn’t based on a scheme.
Charles Wood, Earl of Dorset, thought he was prepared for everything. But falling in love with the woman he pretended to be in love with took him by surprise. After all, he’d come up with the fool-proof scheme to help his friend. He’d promised Mary that no hearts would be affected in the process. It was a promise he had a hard time keeping, but as a gentleman he wouldn’t take advantage of the situation.
Competing with another earl for Mary’s attention was also not something he expected. Though Mary may not have been affected by him, the time they spent together during the London Season has convinced him that his happiness lies in winning Mary over and besting the other earl vying for her affections.