this is probably a big hole in my game; I'll explain it as best I can and appreciate any comments.

I (e.g.) raise from late with AcKs -- this level III of a freeroll multi

The flop has a pair of 8s, two spades and a club, but no real help. It checks around (3 people)

The turn is a K, so I feel like I'm in decent shape. I bet and get called by both.

The river is a spade. Now:

Of course I'm not in decent shape anymore. But I've been waiting for something playable for about 3 rounds. I play tight and aggressive -- sorry to Fnord and everyone who plays marginal hands and wins.

The play most people make with a four-flush on the flop is to bet it big. So I'm halfway ruling that out. I'm halfway ruling out the eight as well, since an eight would've EITHER bet the flop or raised me on the turn.

Having halfway ruled out the hands that can beat me, I call because the pot is rather large now. This is not a bad beat story. It's a me-making-a-bad-play story. Should I just assume someone's got the best hand if I've got the second best?

History:
ANTES/BLINDS
wcda posts blind ($25), super28 posts blind ($50).

PRE-FLOP
shoetech folds, str8 flush40 folds, donn1234 calls $50, NuWere bets $100, bigdadyjohnx folds, davefla folds, nineballqn folds, OHIOFRED folds, wcda folds, super28 calls $50, donn1234 calls $50.

FLOP [board cards 8S,JS,8C ]
super28 checks, donn1234 checks, NuWere checks.

TURN [board cards 8S,JS,8C,KD ]
super28 checks, donn1234 checks, NuWere bets $100, super28 calls $100, donn1234 calls $100.

RIVER [board cards 8S,JS,8C,KD,9S ]
super28 checks, donn1234 bets $325 and is all-in, NuWere calls $325, super28 folds.

SHOWDOWN
donn1234 shows [ 7S,AS ]
NuWere shows [ KS,AC ]
donn1234 wins $1,275.