hero calls down at 50NL

I'm clearing a PSO promo at Paradise. PT doesn't work well (manual hh entry), so no formal stats. It's 5 max.

CO plays a lot of hands, somewhere in the range of 60% VP$IP. He cbets. My plan on the flop was to check/call down.

MP ($15.25 in chips)
CO ($53.25 in chips)
Hero ($48.25 in chips)
Hero: Post Small Blind ($0.25)
Hero is dealt A[img]/images/graemlins/spade.gif[/img] 8[img]/images/graemlins/spade.gif[/img]

MP: Call ($0.50)
CO: Raise ($1)
CO said, "zzzzzzzzzzzz\"
Hero: Call ($0.75)
MP : Call ($0.50)

*** FLOP *** : [ 8[img]/images/graemlins/diamond.gif[/img] 3[img]/images/graemlins/heart.gif[/img] 5[img]/images/graemlins/heart.gif[/img] ]

Hero: Check
MP: Check
CO: Bet ($3.50)
Hero: Call ($3.50)

*** TURN *** : [ Q[img]/images/graemlins/spade.gif[/img] ]

Hero: Bet ($5)
CO: Raise ($10)
Hero: Call ($5)

*** RIVER *** : [ 4[img]/images/graemlins/club.gif[/img] ]

Hero: Check
CO: Bet ($10)
Hero: Call ($10)

Pot: $48.50 | Rake: $2

Fold flop? Check turn? Bet / Fold turn? Fold river? I think river is an obvious fold, not sure why I called.