:grunch:

pre-flop - looks like the villian isn't the only one raising A9o [img]/images/graemlins/wink.gif[/img] (yes, I know you were isolating the button, which is fine - I only mention it because you did)

flop - standard continuation bet. Villian obviously is not scared off...

turn - this just feels like a scare card raise for some reason. My gut feeling is that villian has a higher pair at this point.

river - you're right; the river was weak. Either you believe that he's got the flush/straight, and you check/fold, or you believe he's only got a high pair that you now beat, and you check/raise.