The sum of all kisses / Julia Quinn.

Enhanced descriptions from Syndetics:

From #1 New York Times bestselling author, and creator of the Bridgerton series, Julia Quinn presents the third, stunning installment in the Bridgerton adjacent Regency era-set world featuring the romantic adventures of the well-meaning but less-than-accomplished Smythe-Smith musicians. Following a disastrous duel, a dashing mathematician and a headstrong young lady are at odds--until fate throws them together.

Hugh Prentice has never liked Lady Sarah Pleinsworth, and his opinion is confirmed when he overhears her yammering on about how she must get married this season or she will simply die. He's never had patience for dramatic females, and the words shy and retiring have never been in Sarah's vocabulary. Besides, even if he did grow to enjoy her company, it wouldn't matter. A reckless duel has left this brilliant mathematician with a ruined leg, and now, unable to run, ride, or even waltz, he could never court a woman like Sarah, much less dream of marrying her.

Sarah has never forgiven Hugh for the duel he fought three years earlier, the one that forced her cousin into exile, nearly destroying her family. But even if she could find a way to forgive him, it wouldn't matter. She doesn't care that his leg is less than perfect, it's his personality she can't stand. But when the pair is forced to spend a week in close company they discover that opinions--even those firmest held--can, in fact, be altered. And when a kiss leads to two, three and four the mathematician may lose count and the miss may, for the first time, find herself speechless.