Bad steal attempt?

No specific reads, but something about his bets screamed to me that he didn't have anything. Any reason that pushing back was a mistake? Should I have done so sooner (i.e. on the flop)? I figured me pushing with the J would be believable after the pf raise, leading to a fold.

This weekend made me take back what I've been saying about bluffing the unbluffable. People on party would call so much crap it sickened me.

Party Poker No-Limit Hold'em, $ BB (10 handed) converter

Hero ($15)
SB ($10.9)
BB ($49.25)
UTG ($29)
UTG+1 ($71.6)
UTG+2 ($45.5)
MP1 ($36.5)
MP2 ($69.15)
MP3 ($9.5)
CO ($45.5)

Preflop: Hero is Button with K:diamond:, Q:heart:. SB posts a blind of $0.25.
7 folds, Hero raises to $1.5, SB (poster) calls $1.25, 1 fold.

Flop: ($3.50) 8:spade:, 8:club:, 7:club: (2 players)
SB bets $1, Hero calls $1.

Turn: ($5.50) J:spade: (2 players)
SB bets $4, Hero calls $12.50 (All-In), SB calls $4.40 (All-In).

River: ($26.40) A:diamond: (2 players, 2 all-in)

Final Pot: $26.40

He already put in over half his stack... i don't try to bluff once they are pretty much committed.

- sed

So fold then, even with a "I don't believe you have anything" read? Calling seems out of the question, because even if he doesn't have anything, neither do I...

Should I have reraised on the flop to continue the pf aggro?