The point is that if your spouse has left you, then you have to deal with that, and arguing about what is best for the kids is just another resentment to hang onto, and that's not good for the kids either.
It is what it is. Life isn't always fair or easy. Make the best of it and count your blessings.
The reason why it is important, TH, is that when the WAS goes to a therapist, the therapist does not know not to believe anything they say so takes the word of the WAS that the feelings are irretrievably gone, etc. When that is coupled with the notion that kids are resilient and they will not be happy if each parent is not completely fulfilled and self actualized, the therapists often contribute to the demise of otherwise salvageable relationships. This problem is discussed by MWD and many other experts.