A Certain Magic

Signet Regency, 1991, ISBN 0-451-16916-6

Alice Penhallow and Piers Westhaven had always considered themselves to be best friends--that was until Piers called upon Alice's help and advice in his decision to marry a much younger woman. By the time they realize that it is love that is between them, it might just be too late.

A Certain Magic by Mary Balogh