From (the voyeuristic and poorly-reviewed but often fascinating) The Third Woman: The secret passion that inspired Graham Greene’s The End of the Affair, by William Cash:
There is the clearest evidence that Greene very deliberately looked out for literary connections — taken from his vast reading — through which he identified his passion for Catherine [Walston, the woman on whom Sarah, the fictional love interest, is based]. Every year from 1949 until at least 1955, Greene gave her for Christmas an ordinary hard-backed exercise book ‘love diary’, in which he went to the extreme lengths of hand-writing a literary quotation just below each day of the year; each quote reflected an aspect of their shared literary and religious interests. . . .
The very first quote he writes in Catherine’s diary bleakly reflects the paradox between, on the one hand his rapidly growing fame and on the other, his uncertain love with Catherine. He was often (or so he said) driven close to suicide over her refusal to leave her wealthy husband to marry him: ‘Literature as a rule is the refuge of the miserable. The happy seldom write for writing’s sake; they are fully employed in living,’ runs one quote; a few days later, ‘We are only like dead walls, that ruin’d, yield no echo’; often it is almost impossible to read the author’s name scratched beneath in his tiny ink hand. But again and again, the quotes Green wrote in Catherine’s diaries reflect the very same themes — of love and hatred — that afflict Sarah and Bendrix in The End of the Affair.