Not betting that flop was a huge mistake. The hand probably ends right there and Hero has 6.75 SB more in his pocket than he had before.

After that he's only letting his opponents catch up, and a lot of 6-max players don't 3-bet AJo or even AQo.

By river, CO probably can't fathom that Hero wouldn't have bet an ace on the flop, thus the raise. Call, because although he may have one of the above hands or a spade, it's more likely CO has a weaker ace.