Thanks for the tips and advice, everyone.

I take the point about A9 offsuit being weak, but I confess that if I am on the button on a six player table and it is folded to me, as was the case here, then I often raise with A9 or even less to try and pick up the blinds. Perhaps I am playing too loose and asking for trouble!

On the river when I had the straight, not just TPTK, and he pushed all in, I again take the point that such a player has hit something, but as the flush was backdoored I still couldn't persuade myself that he had it. More fool me!

I'll keep learning.