yucky spot for KK - the draw gets there

Villain is 50/8 and PFA is .25. By the river I knew he had me but I felt pot committed and didn't want him bluffing a draw so I blocked. Any bet pot committed me so I just put him all in. Thoughts?

PokerRoom No-Limit Hold'em, $1 BB (3 handed) internettexasholdem.com

saw flop|<font color="#C00000">saw showdown</font>

BB ($63.75)
Button ($85.50)
Hero ($179.80)

Preflop: Hero is SB with K[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/heart.gif[/img].
<font color="#666666">1 fold</font>, <font color="#CC3333">Hero raises to $4.5</font>, BB calls $3.50.

Flop: ($9) 6[img]/images/graemlins/diamond.gif[/img], 4[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $7</font>, BB calls $7.

Turn: ($23) 6[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $16</font>, BB calls $16.

River: ($55) A[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $36</font>