People have been complaining about George holding grudges. Yes, he could hold a killer grudge. But they seem to be making 4 assumptions that I think are inaccurate:
1) he was wrong to be so angry; 2) he shouldn't have stayed angry so long; 3) he had no provocations after the breakup and 4) he didn't try to get along with J&P after the breakup.
1) People get that George was jealous of J&P, but they seem to think he just wanted more power in the band or was being petty. I think there's a lot more to it than that. As musicians, the Beatles' identities were bound up in their ability to write and compose. If you devalue any Beatle's musical ability, he feels devalued as a person. Furthermore, J&P both looked at George as a "little brother." That might seem sweet, but it's actually demeaning. Imagine that in each interaction you had with 2 of the people you love most, their body language, their facial expressions, and the way they talk to you tell you in no uncertain terms that they don't think very much of you. That would hurt, wouldn't it? And if you valued their judgment, wouldn't you come to believe they were right (while at the same time getting defensive because your sense of self is attacked)?
Now imagine that nothing you do ever changes the demeaning way they treat you. Remember the breathtaking version of WMGGW on the Love Album? That's the demo George played for the other Beatles and George Martin. Imagine you just wrote that. Now imagine that people who make their career by knowing good music when they hear it have just passed over it because you're the one who wrote it, and they don't expect anything from you. George was perfectly aware that the others expected little from him, and by the end of the band, he realized that nothing he wrote would change that. Think about it: he's almost 30 and he's written Something and WMGGW, and J&P still think he's the little kid that followed them around when they were 17. I think that's plenty of reason for him to carry some deep-seated hurt, don't you?
2) The Beatles were practically family. When people carry scars and resentments from family members spending years attacking their sense of self, no one says to them, "Why are you holding a grudge? Stoppit." So how come when the family is the Beatles we look at George's situation differently?
3)"Holding a grudge" means stewing about something that happened a long time ago and isn't continuing in the present. But did J&P ever start treating George differently? After George died, Paul was still saying "he's just my little brother." After 40 years, he still hasn't gotten it. John was more respectful, inviting George to play on his albums. On the other hand he pulled out of Concert for Bangladesh at the last minute, leaving ever-un-self-confident George certain that the concert would fail as a result, because who cares about George, everyone was just coming to see John. (And Bob Dylan, another last-minute question mark, but that's another story.) I'm running out of space, so I'll let you think of more examples. Anyway, there were continuing provocations that brought up the same old hurt.
4) George remained in contact with John; they just fought. Remember, John was an unstable basket case. Maybe George was just tired of saying "Yes, John, it's only you," and finally started to set a few limits (in the sense discussed in the John&Yoko/Paul&Linda thread on johnheartpaul).
As for Paul, how do you deal with someone who treats you like a "little brother" no matter how often you tell him it bothers you? Who seems incapable of realizing that you've grown up, and 9 months isn't that big an age difference, anyway? If George wanted to avoid fighting with Paul, he had to keep his distance. I don't see anything wrong with that. Relatives keep their distance to keep the peace all the time, and no one calls that "holding a grudge."
Remember, George forgave Eric Clapton for running off with his wife, even though it upset him a lot. If he didn't fully forgive J&P, maybe, just maybe, he had a good reason.