I think he's shown all the hallmarks of betting for a draw - could be flush or str8.

I think, considering the pot size, you've bet enough on the flop to make sure he's not getting the odds for his call. Although it is marginal.

If you're not happy to call his big river bet, why did you call the turn bet? I think you should have raised on the turn to find out if he really has the goods.

I would like to think I'd have laid down my three 9's on the turn once he started showing some strength. Easier said than done though .