OP I'm going to have to disagree with you on Lennon. He was 29 when he married Yoko, the affair had started before. For me it has nothing to do with MLC, more to do with many happens when someone becomes famous, the person they were married with, especially if at an early age and while the partner is not famous, no longer fits the famous lifestyle.
Cynthia simply no longer fitted the way John wanted to live. Even if yes, their divorce only happened years after John had become famous. But John had been unfaithful many times before, he was no saint (nor he was while married to Yoko).
And I don't believe Yoko broke the Beatles nor that John did it. The Beatles were pretty much broke because they become too famous, people change, fame and money and drugs change people. Remember they had to stop play live because they could not hear themselves with all those girls shouting madly? That was broke/killed the Beatles.
Lucy in the Sky with Diamonds means LSD. It is one of the songs of Sgt. Pepper's Lonely Hearts Club Band and also features in Yellow Submarine, a record and a film that are perfect acid trips. Also, Lucy was written mostly by Lennon, not McCartney.
Lennon was always unstable and moody and, for all I know, never a happy person. Nor a nice one.
Do you know that Lucy, the australopithecus afarensis found by the Leakeys, is called Lucy because when they found her bones Lucy in the Sky with Diamonds was playing in the radio?
Fictional character of the season going through a MLC, detective Martin Hart from the tv show True Detective. The man messes up big time and still does not get it nor wants to own up to it.
Sometimes good things fall apart so better things can fall together. (Marilyn Monroe)