thanks for the replies guys.

first of all I made a small bet on the flop because I hoped that if he has something like AK or AQ he will interpret that as a probe bet and raise me.
but when he just called i figured him on a monster (ie QQ).
I agree he is not likely to hold KK as he would raise with that after the flop

second, after any bet on the flop even the smallest one I'm almost pot committed.

third, the stacks sizes are mentioned in the example below.

by the way, I checked on the turn he checked also. the river was 3 spade. I went all-in he called and showed QQ .

In his book "Harrington on holdem" harrington writes: "when your sets gets outflopped you're SUPPOSE to lose all your money".