Went down this road about 12 years ago. Only advice I can give is to hire a good lawyer and follow their advice, and document every single interaction you have with your ex from this point on. Write it down, no matter how insignificant you may think it is. Get hard copies of everything that might be important. Don't think that just because it is online, it is safe. You may be tempted to "be the bigger man" and play nice during the proceedings, but at this point it is all about 1) your kids, if you have them, and 2) yourself. Your ex and his/her wellbeing cannot be any of your concern. For whatever reason, they have decided that they no longer want you to be a part of their happiness or wellbeing, so don't feel like you have to do that. It may be a hard habit to break, but force yourself to have a heart of stone when it comes to your ex.
I know it may not seem like it right now, but you will move past it. I got re-married eight years ago and I am happier now than I have ever thought possible.
One last thing, I don't know how old you are, but perhaps you could take this as an opportunity to re-invent yourself. Look at your future as a blank slate now, and do the things you might not have been able to do with your ex. My ex hated to travel, and her idea of a great family vacation was crashing at her brother's place in rural Florida. To this day she has never left the United States. Since our divorce I have lived and worked on two additional continents, and visited 18 other countries. I have hiked in the Alps, enjoyed Argentinean wine in Buenos Aires, walked on the Great Wall, swam in the Persian Gulf, enjoyed St. Patrick's Day in Dublin, and countless other things that I would not have been able to do had I stayed married to her.
Good luck and all the best to you. And don't skimp on a lawyer, even if your ex claims a desire to make it amicable!