I don't MIND the 3 bet on the flop, but... Ugh... CO coldcalling for 3 bets on the flop is a dead give away that he is on a heart draw or a straight draw, perhaps a slowplayed JJ or 99. Either way it's gross that he cold called 3.
I check the turn because all those draws just cashed in and we are still behind to perhaps a slow played set. The pot is pretty sweet now, so I don't imagine folding is an option, but I certainly think checking is better than any other line due to the cold call behind us.
I should also check call the river.
I made a post two days ago in small stakes limit about a bad fold I made with top pair. Folding top two in a big pot... You are getting too good of odds to fold without reads.