One Step More by Jess Draper

Stash has known Carol since high school, and she's the only thing he's ever wanted. Unfortunately for Stash, Carol only wanted women then, and that's all she wants now. Stash will try to make her a 'real woman' using any means necessary, including, for some reason, bedding her girlfriend (a dancer Carol 'keeps' in the city).
'This is the story of the strangest pact ever made between a man and a woman. She was a confirmed Lesbian and he knew it: nevertheless they agreed to have him do everything within his power to change her, to prove to her that a man could give her everything a woman could and more. How he faced this ultimate challenge to his masculinity, and how she reacted, is a fascinating story.'