Hev, Shev and John
The Evelyns got back from their disastrous cruise at the end of May, 1929. Evelyn immediately went off on his own to Beckely to begin Vile Bodies, while She-Evelyn returned to the flat at Canonbury Square. The Evelyns met at weekends in June, but during the week She-Evelyn went to parties, chaperoned by John Heygate who the Evelyns had known since around the time of their marriage a year before. In the middle of July, Evelyn received a letter from she-Evelyn saying that she had fallen in love with John Heygate and didn’t know what to do. 
I’m not sure if the three of them actually met then to have it out. I think not. But Alexander Waugh has told me that Evelyn’s mother’s unpublished diary reveals that on the weekend of July 16, 1929, John Heygate and She-Evelyn drove to Beckley instead of Waugh coming down to London for the weekend. I think that was before the letter though, while things were still ostensibly chummy between the three of them. Anyway, Waugh came to London for a couple of weeks, Heygate was persona non grata, and the Evelyns went everywhere together. But then when Evelyn went back to his self-imposed, novel-writing exile again, She-Evelyn was back partying with handsome Heygate and a picture of the happy couple appeared in the press. Waugh saw it and that was that.
John Heygate had gone on holiday to Europe with Anthony Powell when the latter received a telegram from Waugh saying, ‘Instruct Heygate return immediately Waugh.’ Evelyn had made up his mind that he no longer wanted his adulterous wife. Heygate could have her!
Waugh wrote to Henry Yorke in September about the extent of his hurt. When friends advised Waugh to put it behind him he was quoted as saying, “I can’t, I can’t”. Ironically, in The Scarlet Woman, when the Dean of Balliol (Evelyn) felt let down by the Prince who had fled to the arms of Beatrice de Carrolle, Waugh expressed himself in a similar sort of way, a caption declaring that he (the Dean) had never felt so injured. 
Martin Stannard is good on the Heygate/Waugh love triangle in his excellent 1000-page biography of Waugh. So is Selina Hastings in her invaluable tome. I have emails from Richard Heygate, which I quote from in EVELYN! Rhapsody for an Obsessive Love, giving something of his father’s point of view. So do take a look at that when the chance comes. Oh, yes, and I have photographs of the actual participants, courtesy of Alexander Waugh and Richard Heygate. Not just these actors, splendidly cast as they undoubtedly are.
Next.