The Courtship Dance by Candace Camp

Lady Francesca Haughston had given up on romance for herself, finding passion instead in making desirable matches for others. So it seemed only fair, when she learned she had been deceived into breaking her own long-ago engagement to Sinclair, Duke of Rochford, that she now help him find the perfect wife.

Of course, Francesca was certain any spark of passion between them had long since died–her own treatment of him had seen to that. The way Sinclair gazed at her or swept her suddenly into his arms…well, that was merely practice for when a younger, more suitable woman caught his eye. But soon Francesca found his lessons in love scandalously irresistible–and a temptation that could endanger them both.