Let's be clear, Boston was not a contender when Allen left, which is pretty apparent by the 41-40 record during the 2012-3 season. Boston was cooked. Boston disrespected Allen several times including by trading him (only for Memphis to re-neg), by benching him, and then by signing Terry. Sure they offered him more money than Miami (though no where near what they could have offered), but when you had made 178 million in your career, sometimes money is less important than just wanting to feel loved. Boston failed in making Allen feel loved, so he left for a place that truly wanted him and offered the maximum they could offer.
All of this is true, and probably fair justification for why Ray felt slighted by the organization, and thus left for Miami.
But it isn't justification for the way he handled it, particularly in regards to KG, Pierce, and Doc. Those guys seemingly always did right by Ray. Not returning their calls/texts was clearly a diss, and most likely at the heart of why those three, in particular, still harbor ill will towards Ray. I don't blame them in the least.
As for Rondo and Ray, and their feelings towards each other, well, I'm sure both did things to each other that led to their ill feelings towards each other. They're probably both in the wrong on some level. They just didn't like each other. So, while Rondo probably doesn't have much justification for being upset over how or why Ray left, I don't blame him for not wanting Ray at a party he's putting together. I doubt Ray would have shown up anyway, even if had he been invited.