Here's the thing. While it hurts like hell to have this happen, you can look at it in a way that may lessen that pain. You STILL will see your kids and this CAN make it easier to DB. I know I have posted many a time that sometimes I really wish my W was not around me 24/7 as a CONSTANT reminder of what she did/what I don't have. It takes a different kind of strength to suffer that fate. I know its REALLY hard to deal with the uncertainty of what may be about to happen but please give yourself the solace of knowing that it's just a different path to the same two outcomes, staying together or splitting apart and in my opinion, her leaving does NOT necessarily make it more likely she'll eventually leave the marriage for good.
Grieve what you feel you are losing and then get to the work at hand of rebuilding your life in YOUR likeness, not hers or the family. Work on identifying those parts of you/your life you want to change or grow and then DO IT. Any time you find you have to yourself, FILL IT with things you LOVE to do, even if you don't particularly feel like doing them because of all this. Eventually, you WILL want to and no matter what, even going through the motions will help you learn how to do it for real.
Keep your chin up and please, keep posting. We can help.