It's a difficult path to follow, none of us "Really" know what's best. But the script is so similar that we can often suggest the path with the best odds. But none of us know you, your WW, or OM, so impossible to know if any of the advise is the best way.
I would suggest you not say anything to anyone until you have some sort of proof, because as soon as you do anything, your WW is likely to start changing passwords and locking phone, it will be very difficult to get anything once the cats out of the bag.
take a minute and really think things through, because once you out an A, you can NEVER take that back. There are few things that we LBS can say or do that can permanently change the direction our R is headed, but outing an A has a big impact on multiple people, so just think it through, there's no hurry to decide.
M - 9 1/2 years 5/5/16 - Bomb drop - 3 week EA 10/31/16 - We sold house 01/10/18 - D Finalized