Just thinking some more about this. When you think his father deserted him, his mum, Stuart and Brian all died. I think Cynthia was just a stop-gap. His relationship with Yoko was obviously life-and-death for him. His relationships seem very important to him.
So how was he able to desert and scorn Paul, the one person who you would have thought John would have been the closest?
But I guess it could have been Paul, who I've always thought of as kind of self-sufficent and a bit distant. He didn't need people in the way John did.

yes, John had a lot to deal with in his life....and I do feel really sorry for him and let this be his excuse....but there are times when I just can't accept the way he behaved. In the end he was only human, think I get sick of people putting him on a pedestal, even if this all sounds weird, he's still my favourite one
.....
......wait a minute.....Kevin? wasn't you the one who didn't like John as much? Thanx for defending John   

Quoted from raxo

... I'm not sure if this last photo session was or not their last time together but there were not so many o-port-unities to be all of them together ... for ... for what exactly? ... busy Ness?  ... which one? ...

When did John tell Paul he was leaving the band? ... in September, right? ... Were the other two there too? ... Their "Last Time Together"?   ...

john had told someone during help he was done........

yeah that's true....glad he stuck around for some more years though...

Quoted from pc31

john had told someone during help he was done........

Yeah, he had accomplished what he sent out to do by then and it over whelmed him. We're lucky we got what we did with the lads.