Don't tip him off that you're exposing to the other woman's husband until you've actually DONE it. The whole "friend him on FB" thing is only going to tip the illicit couple off, and they'll try to get their story straight and spin a big line of b.s.
Exposure should always be done FIRST, THEN you confidently own up to what you've done, with a "I felt he had a right to know," and a "Everything I've done, I've done to fight for our marriage."
