The reality seems to be that, from numerous corroborative insider accounts, even while she and John were recording the last album, DOUBLE FANTASY, she was at the tail end of an affair with an art dealer - who was somewhat of a gigolo of a man - called Sam Green, ("She was the best playmate I ever had!" Sam Green explained to biographer Albert Goldman, saying that Yoko would slip away for secret liaisons with him in hotel rooms in between recording her tracks on the album.
Somewhat earlier, while in the middle of this supposed affair, she was preparing to divorce John , telling people that she was "bored" with him and had, at one point, moved John's possessions out of one apartment to another in the Dakota, while John and Sean were in Bermuda, where she had sent them on holiday (after telling John that her tarot card readers thought that the trip would do him and Sean good), and was ready to cut John out of her life when he returned.
(Sam Green, John & Yoko)
Sam Green, perhaps panicking at how fast things were moving and the enormity of this, made her put them back. John's will was also changed to make Sam Green the guardian of Sean in the event of John and Yoko's death.
Her plans to actually divorce John fizzled - or were at least put on the backburner - somewhat when he unexpectedly returned to recording.
And another man she already knew (a bisexual interior decorator) called Sam Havadtoy dropped his boyfriend and moved into the apartment immediately after John was murdered. He explained to his boyfriend that he was now straight and "You don't understand: this is the natural thing to do!".
Andy Peebles, who conducted one of the last interviews with John and became part of the inner circle, said that he eventually realised that Yoko and Havadtoy seemed to have been having a relationship even before John's death.
John, for his part, dismissed both Sam's as "Yoko's fags" and that they were "on the make", not considering either of them a threat in his lifetime.
She lived with Sam Havadtoy for the next twenty years, longer than she was with John and her other two previous husbands combined. Why they eventually separated is unknown, but presumably he had to sign some kind of gagging order when they did so.
I notice that, merchandise wise in the letter, she is already focused on protecting the "legal rights" of the family, re: the exploitation of John's name.
And nobody was ever able to quite figure out where all this money raised for "The Spirit Foundation" charity, quickly erected in John's name went. The charity was vague about where the money would go. "Use the money where we see fit" was the most anyone ever found out.
Both Julian and Cynthia said that Yoko was obsessed with money (and playing a power role) - it was all she ever went on about they said - and that all conversations inevitably came back to money.