it isn't just facebook either. It is total transparency she has to cough up email accounts, cell phones, facebook, twitter, aim, yahoo messenger, skype, multiplayer games with chat features.
I have read enough stories to see how hard cheaters will work to stay in their fantasy. I have read stories where they started with email, then face book, then phone and text, then skype mobile to hide text's back and forth on the phone bill, when one get cut off they move on to another. Hear of them creating a joint email account and self emailing messages back and forth on the one account. IMO you need to look harder otherwise you still have a third wheel in your marriage.
I forgot whether or not you said you exposed this to your friends and family. If you have not do so now. I would contact the boss of the OM at work and HR (if you have one) file a complaint with both of them. Since this guy seems like he is not that important he will likely be let go.
You my friend are at war now. Not with your wife and the OM but with a fantasy world they created. The only way to tear down their fantasy is to inject large amounts of reality. Make the fantasy world ten times worse than the safe and secure marriage she once had.
The time for nice and loving is over. Remember there is a reason why "all's fair in love and war" is such a well known statement.
Right now you are at war with that woman that betrayed you not your wife. You wife is a new relationship junkie right now. I am so sorry your WW put you in this position. However now it is time to Man up figure out what you want. then do what is necessary.
If you want to R do the 180. demand and enforce the NC. Get your selves into MC and IC. Outline several key terms that have to be fulfilled in order for you to consider R. Contact a lawyer and have an initial draft of your D papers at the ready to show her if she waivers. Set your boundaries in the sand and fill them with iron and concrete.
IF you want to D get a VAR and keep it on you at all times. Contact a lawyer and start the paperwork. Don't do anything to make yourself look bad in court ,ie verbal or physical harassment, pitting the kids against your wife, see another woman, or party it up single style . You need to be spotless since you are a man.
ONce the D is final you can call her and tell her who and what she is. What she is worth, and wish her happiness in the fact she found a homeless 23 year old to live a life with. Move on find a LS that's twice as hot and then rub it all in your XW face.
Good luck either way.