The backstabbing isn't fun, I can sympathize with that, although it's a somewhat necessary part of FFA play. FFA games' loyalties can get really fluid and dynamic. It's a turn off and a turn on of sorts.
This is why I generally only play team games, whether it be in civ or in a first person shooter or whatever - no real backstabbing there. If you play FFA, you just have to be prepared for it. I'm sorry if this was an overly negative experience. If it makes you feel any better, you got picked on because you were doing too well. It's sort of a recognition of skill when everyone in the game feels the need to gang up on you. That is fundamentally why we've all invaded at this point.
I'd suggest turning it into a team game if that would make things better. I'd prefer that over your leaving. I also don't have any issues with replaying your turn. If you are sticking with it, I'd prefer a good fight over a quick victory.
I know we don't have PAs or teams set up, but we could bs a team game, I'm sure. We could make it single elimination or whoever wins the space race first for win conditions. If you're too put off already, though, I'd understand.