Lennon was ready to quit back in 1966.
While Lennon was rattled by the "bigger than Jesus" controversy in the United States, and the band as a whole was shocked by the Philippines concert, Lennon wasn't looking to quit in 1966. Rather, it was
Harrison that announced that the 1966 concert tour was the last, and the band, especially Brian Epstein, genuinely didn't know how to continue from there because being a band meant playing concerts. Everyone agreed to take a break and do their own things -- Lennon did some acting, McCartney did some music composition -- and they decided to do an album and see what happened.
Sgt Pepper is what happened.
Being a studio-only band started to feel like a job.
It did, but only in the sense that they didn't know what else to do. It wasn't like they had role models to follow; there wasn't another band who had given up the touring/live aspect.
The Let It Be project was supposed to be them rehearsing for a concert not recording a new album. I think that's the only reason Lennon was even on board even though he was dubious of the Beatles ever playing live again.
Actually, Lennon was quite enthusiastic about the "Get Back" project. They all were, until it dawned on them that 1) sitting in a cold and drafty movie studio wasn't their idea of fun, 2) they had to work to the film crew's schedules and not
their schedules, 3) the studio had always been their creative environment and having others there inhibited that, and 4) showing up for filming was really too much like work. Lennon didn't take the "Get Back" sessions especially seriously, but Lennon didn't take much of
anything seriously at that point.
Despite the famous scene in
Let It Be of McCartney and Harrison sniping at one another, they got along quite well during the sessions, and together they worked out "Isn't It a Pity?" and "All Things Must Pass," two songs that would ultimately end up on Harrison's first solo album. The real tension was between Lennon and Harrison, and Harrison bolted from the band when the two got into a fistfight, which resulted in the band taking a time out, canceling the Twickenham filming, and bringing keyboardist Billy Preston into the band.
Lennon wouldn't decide to leave the band until the summer of '69, when he finally realized that he didn't
need the other three as sidemen any more. Lennon still needed sidemen, he wasn't the multi-instrumentalist that McCartney was (and is), but he could find them easily. And with the other Beatles rejecting "Cold Turkey" as a Beatles single, he moved on.
There are lots of reasons the Beatles broke up. Ultimately, I think they simply needed
space. Not creative space, in the way that George Harrison clearly did, but
emotional space. They had been together, at that point, for over a decade, and their lives had been built around each other. Paul finding Linda, John finding Yoko started the two men off on different paths where johnandpaul diverged in two directions.
Ringo, of course, played with everyone. George worked with John as a sideman on
Imagine, but the Concert for Bangladesh drove a rift between them that never healed. John and Paul very nearly came back together again in 1975 for Wings'
Venus and Mars album. The failure of George and Paul to work together, outside of "All Those Years Ago" (even then done entirely at distance) and the
Anthology is, in my opinion, the great tragedy of the break-up, because it was very much borne of a failure to communicate. John and Paul each needed to find their individual footing, but George and Paul never had a compelling need or desire to work together again.
