At our wedding (which I still allowed him to attend) he started crying to my wife's parents about how much he loved my wife, and so on.
From that day my wife and I stopped talking to him; the two-faced low-life prick, in my opinion.
So recently he reaches out to my wife (I'm told it wasn't the other way around) and they've started talking again.
Suddenly he's decided to divorce his wife.
If she's talking privately with him (text, FB messaging, phone calls) and they are expressing feelings for each other, or even if he's the only one expressing feelings of love and she's continuing to engage, this is an EA. Your best bet if you want to save this marriage is to treat this like the emotional affair that it is and follow the steps in Surviving an Affair to recover the marriage. This will include:
1. Exposure to your family, your wife's family, and the OM's family, and your close friends, asking for support and help in ending their affair. Affairs thrive on secrecy and blowing this up will put pressure on their fantasy world.
2. You do not leave your home. If your wife leaves to stay with her parents, they will hopefully be aware of what she is doing and help put a stop to the affair, knowing that her loving husband wants to save the marriage.
3. Implement a list of precautions in your marriage. No more OS friends unless they are friends of the marriage and see and talk to you two together, not privately.
4. Full transparency in the marriage. This means you know the details of your wife's day, including where she is, who she is with, and what she is doing.