Was the affair public knowledge at the time?

As mentioned, Ralph Roberts (masseuse, chauffeur, and friend) said he knew about it due to Marilyn discussing the solus muscle from the bedroom which she had apparently shared with Kennedy.  However, she only went into detail when the rumours began circulating. She confided to Roberts that it was the only time, and it wasn’t a big deal to either of them.  He said 

“Marilyn told me that this night in March was the only time of her ‘affair’ with JFK. A great many people thought, after that weekend, that there was more to it. But Marilyn gave me the impression that it was not a major event for either of them: it happened once, that weekend, and that was that.”