You are expected to have a PERFECT record of identifying highly skilled, lifelong liars? How do you think they get away with it if the lies are obvious? Don't be so hard on yourself.
I understand though - I was blindsided by Cathy completely turning on me when we moved to London, and finding out so many things she'd told me were lies based on what she told other people about me. You question your judgment of character. But it is a lesson you learned and hopefully you'll be better able to identify the next one.