I'm playing like a rock. Villain is a solid tag on my right and certainly a winning player in this game. 20/5/1 for this session, but he usually plays a bit more agressively.

I think I'm beat. Good fold or stupid?

PokerStars No-Limit Hold'em, $1.00 BB (8 handed) FTR converter on zerodivide.cx

CO ($43.50)
Button ($60.30)
SB ($104.95)
BB ($30.20)
UTG ($55)
UTG+1 ($99.15)
Hero ($114.60)
MP2 ($142.05)

Preflop: Hero is MP1 with K, A.
1 fold, UTG+1 calls $1, Hero raises to $4, 5 folds, UTG+1 calls $3.

Flop: ($9.50) 3, 5, 4 (2 players)
UTG+1 checks, Hero bets $6.75, UTG+1 calls $6.75.

Turn: ($23) 9 (2 players)
UTG+1 checks, Hero checks.

River: ($23) A (2 players)
UTG+1 bets $15, Hero folds.

Final Pot: $38