CO is 55/5/2.3 and goes to showdown 50%, SB is 72/6/0.6 and goes to showdown 35%.

Party Poker 2/4 Hold'em (10 handed)

Preflop: Hero is UTG+1 with , .
1 fold, Hero raises, 4 folds, CO calls, 1 fold, SB calls, BB calls.

Flop: (8 SB) , , (4 players)
SB checks, BB checks, Hero bets, CO calls, SB calls, BB folds.

Turn: (5.50 BB) (3 players)
SB checks, Hero bets, CO calls, SB folds.

River: (7.50 BB) (2 players)
Hero checks, CO bets, Hero calls.

Final Pot: 9.50 BB

with 2 calls on the flop, call me weak but I check check/fold that turn. If there is one caller, then they could have the flush draw but 2 is trouble. what do you beat at the end? only a busted flush draw, straight draw or someone with an 8.

Preflop thru turn played fine.

I think a case can be made for folding or calling on the river. Briachek states the case for folding. But w/ 55% vpip the CO might just be trying to take it down w/ that busted flush draw, or a bare 5 or 8 or even nothing. 8.5 to 1 might be good enough to call that particular player.

well, i wanted a fold on the turn but he bet. Who knows if the CO would have checked or bet the turn if Norton didn't. If he checked behind on the turn, I might lead out on the river again, I might check call. I probably still fold if SB bets or if I check and the CO bets and SB calls.

Well normally with a couple callers here I do give it up, but the fact that these guys are so loose that they will go the the turn and river way too often (despite my raising and the presence of an ace), and the fact that there's a flush draw on board I think are enough to continue betting.

On the river it's nice to see a non-spade hit, and I think the check-call is the best route against the CO. His PFA is above 2 so he's definitely capable of bluffing or betting some inferior hand, and obviously there's no reason to bet into an A. If I was up against the SB, then a check behind would probably be in order.

He showed [8c] and MHIG.

the way you played it, the river is a call as long as you aren't overcalling it. Against a better opponent, this is a recipe for disaster. Good read.