River bluff?
 

Most of my experience is in limit, I haven't been playing NL very long. Is this move -EV over the long run? I had seen villian make some bluffs, but most of what he showed down was either complete crap or top pair, I had not seen him call down with middle pair or anything. Anyway I'm generally iffy about how I played it, thoughts please?
PokerRoom No-Limit Hold'em, $0.50 BB (4 handed) FTR converter on zerodivide.cx

Hero($78.40)
Button ($30.25)
SB ($22.20)
BB ($50.10)

Preflop: Hero is UTG with A[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/heart.gif[/img]. SB posts a blind of $0.50.
hero raises to $2, 2 folds, SB (poster) calls $1.50.

Flop: ($2) 8[img]/images/graemlins/heart.gif[/img], 3[img]/images/graemlins/diamond.gif[/img], 2[img]/images/graemlins/heart.gif[/img] (2 players)
SB bets $0.5, hero raises to $4, SB calls $3.50.

Turn: ($10) 9[img]/images/graemlins/club.gif[/img] (2 players)
SB checks, hero checks.

River: ($10) J[img]/images/graemlins/club.gif[/img] (2 players)
SB checks, hero bets $8, SB folds.

Final Pot: $18