Do you think the river fold was pretty decent?
In my experience after I bet the turn and can have all the hands that I do, why would he lead the river as a bluff?
I don't think I can ever be winning here and I do think he can play a set this way.

Player 5(SB) $10.05 - VP:50 PFR:0 AF:1.0 W:0| STL: 3B:0|0 CB: N:3.95 Hands:2
Player 6(BB) $7.49 - VP:43 PFR:14 AF: W:50|100 STL:100| 3B:0| CB: N:0.88 Hands:7
Me(BTN) $10 - VP:21 PFR:16 AF:2.4 W:25|61 STL:49|78 3B:5|59 CB:53|54 N:-0.64
Player 1(UTG) $10 - VP:0 PFR:0 AF: W: STL:0| 3B:0| CB: N:-0.40 Hands:8
Player 2(MP) $10.67 - VP:63 PFR:25 AF:Inf. W:50|0 STL:33|100 3B:0|100 CB:0| N:-0.06 Hands:8
Player 3(CO) $12.65 - VP:50 PFR:38 AF: W:50|0 STL:50|50 3B:0|0 CB:0| N:-1.50 Hands:8


Pre Flop: Me(BTN) with [A,K]
Player 1(UTG) folds,
Player 2(MP) calls 0.10,
Player 3(CO) raises 0.40,
Me(BTN) raises 1.20,
Player 5(SB) calls 1.15,
Player 6(BB) folds,
Player 2(MP) folds,
Player 3(CO) calls 0.80


Flop: (3,8,4)(3 players)
Pot - 3.80
Player 5(SB) checks,
Player 3(MP) checks,
Me(BTN) checks


Turn: K (3 players)
Pot - 3.80
Player 5(SB) checks,
Player 3(MP) checks,
Me(BTN) bets 1.60,
Player 5(SB) calls 1.60,
Player 3(MP) folds


River: 9 (2 players)
Pot - 7
Player 5(SB) bets 3.50,
Me(BTN) folds