Heather, you need to make sure that Queen B stays in the hive. Dont let your H's actions cause you to have your emotions take over you. This situation will change you, but try to have it change you for the better.
One thing that you might want to read is about forgiveness...
If and when you and H start to haggle over the financial's of a D, it is imparative that you DO NOT use the kids as a leveraging tool in that. Custody arrangements are totally unrelated to the splitting of assets and spousal/child support. Just remember that the kids are the one most losing out and they are the #1 priority in all of this. If your L does not express this as the #1 concern, then find a different L.
Does your state require any parenting classes so as to get a D?