Think about these two lesser the evil situations and let me know your answer.
Situation #1. Your W puts your children first before her PERCEIVED happiness and ends her A and calls off the divorced. You stay married for the sake of the kids but she never becomes fully committed to you again because she believes there is something better out there. You spend the next 15 years wondering if she files again after your youngest is out of the house.
Situation #2. She continues with D and continues relationship with OM. You take time to heal and continue to better yourself. After the dust settles and your emotions start to stabilize you start to realize that your ex had many flaws that you didn't see. Once healed maybe you start another relationship with a woman who is way better then your ex in all aspects of life. She likes to work through problems not run from them. Maybe your ex comes to her senses and wants to reconcile and will do anything to EARN another chance with you.
I don't know about you but I would take option 2 everyday and twice on Sundays. Yes it's a risk that she doesn't come back , but she has to choose to be with you for it to work out long-term.