Full Tilt No-Limit Hold'em, $1 BB (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

MP3 ($55.60)
CO ($86.15)
Button ($64.90)
Hero ($98.70)
BB ($144.50)
UTG ($82.55)
UTG+1 ($157)
MP1 ($100)
MP2 ($63)

Preflop: Hero is SB with K, K.
5 folds, CO calls $1, 1 fold, Hero raises to $5.5, 1 fold, CO calls $4.

Flop: ($11.50) 4, 5, 2 (2 players)
Hero bets $7, CO calls $7.

Turn: ($25.50) 7 (2 players)
Hero checks, CO bets $16, Hero calls $16.

River: ($57.50) 7 (2 players)
Hero checks, CO bets $21, Hero folds.

Final Pot: $78.50

He played this pretty strong. I felt like I was beat. Was this a weak fold?