We warned you to lock your PC, and yes I very much think he's trying to spy.
He may have even found something of yours and you don't know yet.. that may be the source of the smile on his face.
Remember he's addicted, its not him manipulating you, its the addiction.
He may just be playing a save face game, or he may have gone undeerground again.. you do need more INTEL.
I would keep the exposure up.
You could even just keep exposing and talking as if he hasn't ended his affair to see how he reacts.. its a bluff, but it may just cause him to give himself away. He might accuse you of reading his mail and then you've got your answer.. he's been cheating and it is in his email.
He's made no offer of transparency, i would include that in your blanket statement
5. In order to feel safe, I am going to review email and phone records for a while.
etc
Is there someone else who can follow him during lunch? He is most likley to visit her when he knows you are busy at work, so if you can get someone else to watch him or watch the OW then you have an alibi and he will be less careful during that time.
One thing Puppy has done in the past is the GPS in the car... he hid a phone in his car and recorded the convo's in the car and his wife didn't know... he got a lot of info that way.
