Dear Joanna,
You put yourself out there on a limb and asked the question. He sawed it off and you think you were at fault?
Please Dandy Girl, don't put yourself down for this. We all think too much of you here on this board to see you treat yourself this way and not call you on it. You did nothing wrong! Mistakes and misunderstandings happen, and yes, sometimes they can be extremely embarrassing.
In this case, however, I think he is to blame. You asked a question, which is the only way you had of finding out about him. Remember that he didn't wear a ring, never mentioned he had a wife, and came into your shop often for flirty talk. Be glad he told you when you asked him out for a drink. He could have just as easily continued the game and you could have gotten hurt worse.
There are many positives here to look at. Write it off, learn from the experience, and move on.
Tammy