Sounds like things are going better, but also getting harder, for you. I think this is to be expected--you've put your R needs on hold for a long time and worked very hard.
In DR, Michele talks about letting your spouse have mourning time for loss of OW, even letting his sadness be OK. Maybe he has finally decided to let her go and is feeling down?
As for when you will feel safe and quit worrying if you're being duped, it will probably take a long time and a husband who really wants to make your feel secure, and to take responsibility for what he's done. It doesn't sound like he is there yet. Don't forget the baby steps--and GIANT steps--you've made so far though.
I'm sorry you are having such a hard time. Having been through years of doubt during an earlier crisis in my own M, I know how painful it is, and how scary it is when you worry about the fear ever going away.
Don't forget the baby steps--and GIANT steps--you've made so far though. 
