25NL: KK vs a possible flush

Full Tilt No-Limit Hold'em, $0.25 BB (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

SB ($26.70)
BB ($13.40)
UTG ($24.25)
UTG+1 ($36.45)
MP1 ($49.95)
MP2 ($43.60)
Hero ($34.40)
CO ($2.75)
Button ($24.90)

Preflop: Hero is MP3 with K, K.
1 fold, UTG+1 calls $0.25, 2 folds, Hero raises to $1.25, 4 folds, UTG+1 calls $1.

Flop: ($2.85) 4, 3, 3 (2 players)
UTG+1 checks, Hero bets $2.4, UTG+1 calls $2.40.

Turn: ($7.65) J (2 players)
UTG+1 checks, Hero bets $4, UTG+1 raises to $12, Hero calls $8.

River: ($31.65) Q (2 players)
UTG+1 bets $20.8 (All-In), Hero ???.

villain was 22/12/1.6.
I've been stealing some pots pre-flop and post flop.
Was my turn call very bad? Actually, I think I gave away the fact that I was not sure of my hand as I took a while to call the turn raise, therefore, he could shove often and have me fold ...
However, he might still have 44/JJ/QQ or a flush ...
I suppose calling this river is bad?

Villain is 22/12/1.6, so fairly active but pretty passive overall.

Your thinking has got to be off here, he pretty much can't have JJ/QQ because he limped UTG+1. If somebody is raising 12% of hands they almost have to be raising JJ and QQ preflop. 33/44 for a limp, maybe.

The postflop check-call, check-raise line is one of the strongest "I HAVE A HUGE HAND" lines in all of poker. It really looks like it because he magically comes to life on the turn, and it seems like he really wants you to pay off with some sort of second best hand (AA/KK, low flush etc).

You are effectively 140BB deep and pushes roughly 80bb on the river, which to make makes it even more evident that he has something that definitely has you crushed. The only thing I can see him having that you could beat is like AsQo.

Unless he's spewing off a huge stack (has he lost any big pots recently?)and you have identified him as being on tilt with some bad play, my money's staying out of the middle on this one.

I'm wondering if this is a good spot check the turn behind and try and get some value out of weaker hands on the river. Opp's limp/call and c/c out of position on the flop suggest a middle pair like 88, a flush draw or a monster. I don't think many hands we beat call the turn bet, and no better hand folds.

As played, fold to the turn - you have the second nut flush draw on a paired board and opp is showing some serious strength.

yeah that turn call was spew, you only beat a bluff

Yup, the turn call was bad. As the pot is small on the turn, I think I should have checked to keep the pot small and call a fair amount of rivers ...