The rest of the hand history would be helpful, but this is my thinking of the hand. The flop comes with a possible flush draw, a king pair beating the nine I connected. I'm feeling like I'm most likely an underdog at this point. If he checks I know he did it for one of two reasons. One he connected and wants to trap me, or he missed and wants to see the river. I have a feeling, however, that your opponent is a skilled player, and therefor it is most likely he connected on some level. But for this discussion lets say no matter what happened you got to the river while keeping the pot small. You make two pair. If he bets in this situation first I probably fold because he still could have two pair himself with the king pair, or the flush. If he checks, I probably would bet for value thinking I'm now a favorite. If he calls then I wait for the river and play strongly as I hit the full house and try and take him for as much value as possible. I don't think I would have gone all in.