In 1997, just after Mark married Kitty, The Daily Mail ran an article about Mark and the story behind R&J. It was on the Tomas Gygax site and I scanned the article, which was about 4 pages long! In the article it states that R&J was written about Kathy White (Mark's first wife) and his heartbreak when she left him to live with a teacher and also had a child, consequently Mark and Kathy were divorced.
I don't know whether to believe this story - it was written in a very Mills and Boon style, but the words of R&J do fit in more than the situation with Holly Vincent IMO. I still have the article and it makes good reading, but true.......??