[sahaguje]

Funny you did not bet that flop in last position. You dont risk that much : with this board, a set would have bet, and you dont want to give a free card to a draw here. Even if somone has 2 pairs, you still have a lot of outs.
On the turn, OK. If SB was deeper, I would have raised a fair proportion of times if I know he can fold 2 pairs, cause there is a good chance he does not have a very big hand, and even if he has a set you still have outs.
On the river, I dont know. You wont be called with many lesser hands, the A is just too threatening, cause a lot of hands with a black A suited and a 2, 3, 7 or 8 would have called the turn bet, as you did. I can only see you beat a A3 or a A2 with the Ac. Most of the times, you bet will only be called by A8 or A7. So unless SB is a very bad player who'll pay with 87, I would check behind.

sahaguje