AJs on Button

[Catsailor]

Grunch:
I always suspect a steal after all fold to CO. 3B preflop and see if he caps or calls. With the same flop action I think you are outkicked.
Turn: He bet into you again so I think we're behind to his AK or AQ. I would call down unless I hit my J since pot is large.
I think your aggresion caused his Riv check and call. Or maybe he has KK or QQ. A call down will give you a better read on him for next time.
Cat