kk in a big pot

[stu-unger]

reads on villain go something like this. he is a complete maniac/donk. willing to call large raises pf with almost any 2, willing to bluff in most any situation and makes some questionable calls. i have played 2 big hands with him already, one he raised and i reraised with KK in position. the flop was 7 high. he led and i pushed over the top. he called with A7. the other i open raised with 99. he led on the flop with an open ended st8 flush draw and i pushed over the top with the nut set. he called and my hand held up.

50nl 6-max
effective stack 110
dealt to hero on button K [img]/images/graemlins/club.gif[/img]k [img]/images/graemlins/spade.gif[/img]

pre flop: UTG raises to 1, villain calls in MP, hero makes it 5 to go, both call.

flop (15): J [img]/images/graemlins/club.gif[/img]3 [img]/images/graemlins/diamond.gif[/img]3 [img]/images/graemlins/club.gif[/img]
UTG checks, villain bets 15, hero calls, UTG folds.

turn (45): 8 [img]/images/graemlins/club.gif[/img]
villain bets 43, hero calls

river (131):2 [img]/images/graemlins/club.gif[/img]
villain checks, hero checks?

i know my turn call is a little questionable but, i didn't think i was beat yet and i didnt want to push and find out i was. should i push this river or just check and take a free showdown.