Sadly, goldengirl, there's a lot you don't know about people until you get closer and closer to them.
If you had told me 5 years ago that my XABF was an abusive alcoholic I would have laughed in your face - but here I am.
The important thing is to recognize that it's not your fault. You took them at face value, and gave them the benefit of the doubt. With the average person that's a good thing to do (otherwise you'll alienate everyone), but with some people it doesn't work out, and it's hard to tell until you invest the time.
Now that you recognize it, though, you'll be prepared to prevent any "next times"!