McCartney sued the other Beatles because he tried to forewarn them about signing a bad record contract....this really hit them hard and created a huge riff
that and McCartney trying to keep things going, George wanting to quit (limited input), them no longer wanting to tour, John and the Yoko thing and really stepping away from the Beatles for several albums
John and Paul had a very strained, of and on, relationship for most of the time from the last album until John's death
RIP Bucky - 7/25/1943 - 1/19/2013