He all of a sudden wakes up on the river when the third diamond hits and with a AF of 0,4 hmm, I don't think he is bluffing. At the very best for you, he hit his K here. I think I call behind here since his pattern smells alot like a flush draw. But looking back at his river action, the call behind seems strange.
PokerStars 0.10/0.20 Hold'em (8 handed)
FTR converter on zerodivide.cx
Preflop: Hero is CO with K[img]/images/graemlins/club.gif[/img], J[img]/images/graemlins/club.gif[/img].
UTG calls, <font color="#666666">
3 folds</font>, <font color="#CC3333">Hero raises</font>, <font color="#666666">
1 fold</font>, SB calls, <font color="#666666">
1 fold</font>, UTG calls.
Flop: (7 SB) 3[img]/images/graemlins/diamond.gif[/img], Q[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, UTG checks, <font color="#CC3333">Hero bets</font>, SB folds, UTG calls.
Turn: (4.50 BB) Q[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, <font color="#CC3333">Hero bets</font>, UTG calls.
River: (6.50 BB) K[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG bets</font>, Hero...
That makes the check easy to be honest.