Worst fold decision ever?

[John Deere]

Party Poker 3/6

Hero has AA in LMP.

EP limps. MP raises. Hero 3-bets. EP calls, MP calls.

Turn: 3 6 9 rainbow

EP checks, MP bets, Hero raises, EP 3-bets, MP caps. Hero folds.

Am I a total idiot? I couldn't imagine that EP would check-3-bet with anything other than a flopped set (or two pair, maybe, but I find that unlikely). What do you think?

[Alobar]

I dunno about the worst ever, but yeah thats pretty bad. There are quite a few hands he could have that you may be ahead of, or have the odds to draw out against