Good blind D, or awful poker?

[dogfishhead]

SB is essentially an unknown (~75 hands, fairly passive so far).

Paradise Poker 0.50/1 Hold'em (9 handed) converter

Preflop: Hero is BB with 6[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/heart.gif[/img].
UTG calls, <font color="#666666">5 folds</font>, Button calls, <font color="#CC3333">SB raises</font>, Hero calls, UTG calls, Button calls.

Standard, or do you let this go against a relative unknown who hasn't shown much aggression?

Flop: (8 SB) A[img]/images/graemlins/diamond.gif[/img], 6[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">SB bets</font>, <font color="#CC3333">Hero raises</font>, UTG folds, Button folds, <font color="#CC3333">SB 3-bets</font>, ...

Here's where I think I screwed up. The pot is large, so I don't want to let it go having caught a tiny piece of the flop. My (flawed?) thinking is that I might get hands like A5 or K5 to fold behind me, cleaning up 3 outs. I feel like SB probably has me beat, and I'm sure of it after he 3-bets.

Should I fold this flop? If not, what's my line after the 3-bet?