Make-Believe Love — Penelope Butler

When Nicholas begged his childhood friend Adrien to come over to France to nurse his critically ill wife, Gillian, he didn't know what torment he was to put Adrien through. She had never loved anyone other than Nicholas and, although she did her best to conceal her feelings from him, Adrien found it became daily harder not to arouse Gillian's suspicions. Then Gillian's doctor, Raoul Dubois, out of concern for his patient's peace of mind, suggested that Adrien should pretend to be engaged to him. All very well for a temporary measure - but where would it leave her in the end?