Call her on her statements such as "it will never work because you are so paranoid". The fact that she's hiding it so much is a good sign...means she's scared of being caught. If she didn't care for you at all she'd do the other cheater maneuver which is "I'm already emotionally divorced from you anyway".

I would say, "know what? I'm not stupid. You are right...it isn't going to work between us, because a marriage needs TRUE openness and honesty. I really can't believe you would insult my intelligence like this. Have you decide where you are going to live yet? You should probably start looking if you haven't already."

You cannot be lonely if you like the person you're alone with. Dr. Wayne Dyer