Epoh, not to repeat myself, but I still think that you should see a specialist who can rule in or out autism spectrum disorders. That fair/unfair thinking, the anxiety, and the catastrophizing (unrealistic thinking about possible negative outcomes of a test, for instance) are pretty classic ASD issues. FWIW that collection of symptoms doesn't sound like bipolar to me either, though of course from this distance I can't tell you much.
You can do a lot to work through anxiety using CBT methods. Martin Seligman's "learned optimism" strategies do really help with thinking your way out of anxiety, and can be taught to a child your DS's age. A CBT practitioner will have more strategies too.
You can work through social situations the same way, focusing on likely outcomes and possible choices your DS could make. ("if tommy cuts in line, what's likely to happen if I make X choice to respond to that? what happens if I make Y choice? Which choice is better?") Sometimes it's hard to learn to accept the unfair and not make a big deal about it; but it can be learned.
HTH
DeeDee
