How bad was this play?

[maxpower72]

Let me start by saying that I am not a good tournament player but for some reason I found myself on the final table of a 400 person tournament.

There are eight people left with the chip leader having about T 100000 in the big blind and I have T 68500 in the cut-off I am in third. There are two or three people short stacked and the blinds are 3000 - 6000. The chip leader is very aggressive I have been on his table for a while now.

It is folded to me in the cut-off I have KJ of spades. I raise to 18000 to try and steal the blinds, everyone folds to the chip leader in the big blind he calls uh-oh?
The flop comes J 8 5 two spades. I have top pair good kicker and the flush draw. He bets 15000 into the 21000 pot. So the pot is 36000 and I have 50500 left. My choices here I think are to go all-in or fold?