I hate to say this but (currently I'm in kind of 'revenge' mode!)
but it's rare to find a scenario that is primed and ready for a complete destruction of wayward spouse and OM/W as yours is
Just get your facts together quick save eveything and blow them both to kingdom come infront of your family as well.
You're in poll position to
wipe out any denials by your husband so strong is your evidence
to humiliate him (as needs to be done) in front of family
to wipe out, with evidence, the OW
to save the marriage / nightmare of OW fiance
to probably get her fired from work
that will stop their affair dead in it's tracks
that will make your decision making for the future easier
All with one hit - almost Godfather style !
I shoud'nt make light of it I know as this is serious sh!t we're talking about
BUT you really have an opportunity here most of us did not have in this position and you may regret not taking it.
I also guarantee you to have a smile on your face when the **** hits their fan