With blinds that small and so many people at the table, I would have PFR at least 100 chips.

That flop isn't a great flop for you, as 3-4 can make a wheel. Anybody out there with A5 has a chance to make a straight or at least draw another ace. Less likely, someone can have 56. A bigger PFR will drive these hands out.

On the flop, you didn't quite bet enough to scare away draws. With SB having a stack more than twice as big as yours, you can't let him have free cards. I would have bet the pot there.

Scary card at the turn. very coordinated board at this point... someone could have made a straight or be drawing to one, or now has a flush draw, or both. When SB bets, the pot is nearly 600 and you only raised it 400. So now SB sees a pot of 1000 chips and only needs to call 300 for it. Those are pretty good pot odds. Your raise basically sweetened the pot for him. Almost half your stack is in the pot now. There is a possibility that he made his wheel here (A-5 straight) and is just trying to milk more money out of you.

River comes. Your bet of 500 doesn't do anything here... Either he doesn't have a hand and throws it away and you get nothing extra for the bet, or he has already made his hand and will take away the rest of your chips. He raises your bet and your forced to call with the rest of your chips.

Noticed how you ended up putting your whole stack in the pot with just a pair? By betting weakly you constantly dribbled money into the pot, giving him incentive to stay in. A stronger bet before the flop or on the flop would have kept you out of this predicament.

I think this a classic example of what happens when you try to slow play a monster, especially against a player with a stack twice your size.

What were the results? I bet he either made a straight (A-5 most likely) or flopped a set, in which case you were toast anyways.