This sort of thing ought to hurt, nothing wrong with a few tears. Letting your daughter see who you are, your struggles and how you overcome them, might be one of the most valuable things you can teach her. She needs to know that a lot of days we just play the role of who we think we ought to be, regardless of how we feel. Hold onto the good things you have right now. Your daughter, friends, career. Don’t do something stupid like waste any more of your energy on someone who doesn’t deserve it. Have a personal funeral for your marriage. Look at pictures, remember the good times (they were real), cry, then bury it. Be cool, calm, and collected around your ex. Get everything in writing and don’t be alone with her.