[Nick C]

I think the turn raise means you're most likely behind, but unless CO is very passive postflop, I don't think he has to have two pair or better on the turn. He could just have something like A9 that he waited until the turn to raise you with. Of course, other hands such as 66 and T8s and 77 are also possible.

Still, I think you're good often enough on the river to call him down, even though your hand didn't improve to what you actually wanted it to.