Once for All Time by Betty Neels

Clotilde Collins has worked with Dr. James Thackery at busy St. Alma's Hospital in London for three years, but she's never considered their relationship as anything more than solidly professional. Then tragedy strikes and James steps in to take charge of Clotilde's shattered world, offering her his unhesitating comfort and support. How easy it would be to fall in love with him.

Except he's already committed to another woman...