Some thin river value at 1/2 vs unknown

[Renton]

Im 15/12 and pretty aggressive postflop

No Limit Hold'em Cash Game - $1/$2 Blinds - 8 Players - (LegoPoker HH Converter)

SB: $198.00
BB: $214.35
UTG: $289.60
UTG+1: $248.85
Hero (MP1): $391.25
MP2: $219.45
CO: $33.15
BTN: $197.00

Preflop: Hero is dealt 5[img]/images/graemlins/diamond.gif[/img] 5[img]/images/graemlins/heart.gif[/img] (8 Players)
2 folds, <font color="red">Hero raises to $8.00</font>, 3 folds, SB calls $7.00, BB folds

Flop: ($18) 6[img]/images/graemlins/diamond.gif[/img] 8[img]/images/graemlins/diamond.gif[/img] 5[img]/images/graemlins/club.gif[/img] (2 Players)
SB checks, <font color="red">Hero bets $14.00</font>, SB calls $14.00

Turn: ($46) K[img]/images/graemlins/spade.gif[/img] (2 Players)
SB checks, <font color="red">Hero bets $36.00</font>, SB calls $36.00

River: ($118) 4[img]/images/graemlins/heart.gif[/img] (2 Players)
SB checks, <font color="red">Hero bets $72.00</font>

Pot Size: $190.00