I didn't know he was married...

I met this man at the hotel I work at. He stays often on business. He would go out of his way to come by and chat for a bit when he was there, and after a few months he asked me out. We went out on several dates before we slept together...that was a few weeks ago. I just found out three days ago that he's married, he acted like I should've known and that it wasn't a big deal, even though he doesn't wear a wedding band and has never mentioned his wife. I feel hurt and ashamed, not only because this guy I was into turned out to be an asshole but because this woman has no clue. I would never knowingly sleep with a married man, I find it despicable.