villain is unknown. I was tempeted to try float and bluffing line in later streets. Do i have to give up ? If i follow up, how much do you guys think i should bet to get him off and save some money just in case he has real hand?

PokerStars Pot-Limit Hold'em, $1.00 BB (8 handed) Poker-Stars Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

UTG+1 ($100)
MP1 ($78.50)
MP2 ($99.90)
CO ($115)
Hero ($93.50)
SB ($95.85)
BB ($99.75)
UTG ($34.40)

Preflop: Hero is Button with 5, 5.
4 folds, CO raises to $3.5, Hero calls $3.50, 2 folds.

Flop: ($8.50) 6, J, 8 (2 players)
CO bets $4, Hero calls $4.

Turn: ($16.50) K (2 players)
CO checks, Hero bets $10, CO calls $10.

River: ($36.50) 8 (2 players)
CO checks, Hero ??