Blind steal turned into bluff

[Abelardo]

$0.25/$0.5 No Limit Holdem
6 players
Converted at weaktight.com

Stacks:
UTG (<font color="#0000cc">$47.70</font>)
UTG+1 (<font color="#0000cc">$55.90</font>)
Hero (<font color="#0000cc">$65.75</font>)
BTN (<font color="#0000cc">$7.60</font>)
SB (<font color="#0000cc">$99.35</font>)
BB (<font color="#0000cc">$41.90</font>)

Pre-flop: ($0.75, 6 players) Hero is CO T[img]/images/graemlins/heart.gif[/img] K[img]/images/graemlins/club.gif[/img]
<font color="#777777">2 folds</font>, <font color="#cc0000">Hero raises to $2</font>, <font color="#777777">1 fold</font>, SB calls $1.75, <font color="#777777">1 fold</font>

Flop: A[img]/images/graemlins/heart.gif[/img] 4[img]/images/graemlins/heart.gif[/img] 7[img]/images/graemlins/heart.gif[/img] ($4.5, 2 players)
<font color="#cc0000">SB bets $2.5</font>, Hero calls $2.5

Turn: 4[img]/images/graemlins/spade.gif[/img] ($9.5, 2 players)
SB checks, <font color="#cc0000">Hero bets $7.5</font>, SB calls $7.5

River: 9[img]/images/graemlins/spade.gif[/img] ($24.5, 2 players)
SB checks, <font color="#cc0000">Hero bets $19.25</font>, <font color="#777777">SB folds</font>

This guy has vpip over 50 and seems aggro too, but I don't have conclusive evidence (around 70 hands, agg factor over 2).
The flop is kinda bleh and probably should have folded there, I'm folding to further action and betting if checked, he called oh well, but still no hearts, I get checked and I think he has pair and draw or perhaps only the K[img]/images/graemlins/heart.gif[/img] so I fire again big, good, bad, ok?