Very sorry to hear about your sitch - my W is in MLC mode for a year now so I know what you're going through. She started this "dance" in early 2010 and after moving into the other BR and saying she wanted to separate, I too had to deal with her acting out on FB. She changed her status to single, posted candid messages about what she was feeling, and hurt and embarrassed me terribly. I had friends and relatives clue me in as I chose to stay away. Long story short, I was able to get her back and reconcile after a couple months by using DB techniques (even though I hadn't even heard of Michelle and DBing at the time!!), but she gradually changed her mind again and moved out in early Oct.
As to his 'erratic behavior,' I think you'll hear from others that it's to be expected from someone in the throes of a MLC. It's almost as if an "alien" has inhabited his body somehow . . . . . he is not thinking in the manner you are used to and I'm SURE is not making rational decisions. A MLC is a very emotional time for those who go through it, and for those they hurt in the process. Best advice I can give is to read the Divorce Busting book and MOST OF ALL, read and put in place the "180 degree list," which you can find easily online (google it). An important item on that list is near the bottom, where it says "Do not believe any of what you hear and less than 50% of what you see. Your spouse will speak in absolute negatives because he/she is hurting and scared." I urge you to keep that in mind. I'll pray for you, as I pray everyday for my own wife and family. Hang in there. marcusko