MP is ok, but we don't have much history. SB is a donk. Sometimes I bet this flop but I decided to check here, maybe a mistake. I raised turn cuz SB is trying to take it down here with ATC and MP can call with such a wide range, most of which I am ahead of.

And now he fires at the river. I really only beat bluffs basically. It looks like he slowplayed a set of nines maybe or hit a set of 6s on the turn but that's less likely. If he has A8 or A9 and decided to slowplay I think he would have raised the turn himself.

I have to fold here right? Now I am not so sure.

Full Tilt Poker, $0.50/$1 NL Hold'em Cash Game, 6 Players
LeggoPoker.com - Hand History Converter

BB: $43.20
UTG: $18.25
MP: $100
Hero (CO): $139.75
BTN: $393.20
SB: $60.35

Pre-Flop: A J dealt to Hero (CO)
UTG folds, MP raises to $3.50, Hero calls $3.50, BTN folds, SB calls $3, BB folds

Flop: ($11.50) A 8 9 (3 Players)
SB checks, MP checks, Hero checks

Turn: ($11.50) 6 (3 Players)
SB bets $6, MP calls $6, Hero raises to $17, SB folds, MP calls $11

River: ($51.50) 8 (2 Players)
MP bets $28, Hero