Now is the time to get your hands on a copy of "Divorce Busting"..ASAP and follow it's advice closely. I did this three years ago and my partner and I were eventually reunited, in large part because of the work I did using that book, thank you very much. We have other issues now, but that's another story.
Back to you. Don't panic about the divorce. The best thing you can do now is to be a supportive husband and father. Be strong in yourself and your commitment to the marriage. I know it's hard, believe me, but DON'T ask/beg her to stay. Just let her know through your ACTIONS that you are a very important part of her life (whether she admits it now or not), and leave it at that. Don't initiate any conversations about the relationship. When she comes to you, and she will, do alot of careful listening, without asking for or telling her what you want/need. Save that for when you have both agreed to reconcile. It sounds like right now, she is in a very reactive, depressive state. Don't react back. Keep your cool and TAKE CARE OF YOURSELF, primarily for your own sanity and secondarily, because this may give her pause. Depressed, unhappy people are drawn to strong, healthy and happy people. So do that for yourself and for your marriage. When I did this three years ago, it was the turning point both for me and for my relationship. I read alot of Dale Carnegie. Do things on your own or with friends. Get a life. Remember that these things are like marathons, not sprints. Come to the forums often for support and get the book! Let us know how it goes. GOOD LUCK!