Talk to your atty about a restraining order keeping these other people away from your daughter. It may be very difficult, and probably impossible for anyone other than OM himself.
You need to [censored] or get off the pot, pardon my french, CD. Either expose now, or wait until right before she leaves, as we all advised. But you're getting into it with your wife, it's tipping your hand, and it's not productive.
Good job, btw, on enforcing the boundaries about your daughter. THOSE do need to happen, and you handled it very well.
I like the script at the end. Drop those bombs as she leaves for her illicit rendezvous, and watch her spin! Infidelitus interruptus.