Personally, I'd tell her. I'd bust it open, and realize it's going to be a really choppy ride for a while. Like enormously bad. But the truth will expose the lies and deception, which will have to end sooner or later.
Her threats are a barking dog. Don't let the threat of D be a determinator of what your action should be. Do what is true and right, and realize you'll conscience will thank you later.
It is a tremendously awkward situation. I would understand you not saying anything yet.
The truth shall set you free. Keep posting.
M46, EXWW46 M15 T17 D20, S19, D13 M - Addiction since 1998 W EA/PA #1 2013/2014 W EA #2 June 2015... BD 1 Big D talk 9/15 BD 2 - EA/PA disc 10/30/15 Served D 1/22/16 Divorced 5/25/16 (yes, that fast!)