After looking through the game, this appears to be a case of two players attacking the strongest. You accused them in Round 7. At this point, Red had 33 regions, and was deploying 22, green had 31 regions and was deploying 15, and you had 57 regions and were deploying 38. You were clearly the leader in this game, and the two weaker players were simply trying to even the playing field. This doesn't mean they were colluding together in secret, it's common courtesy in 3 player games for the two weaker players to attack the strongest. Add in the fact that this is the only game they have played together, I am Clearing them of Secret Diplomacy.