Would it have been inconvenient to have let your W have the kids for that party? Or did you not let her have them out of spite? I would think you could negotiate and co-parent together better.
You need to lose the anger and blame. It will get you no where. Remember, when you argue with a woman, if you lose you lose and if you win you still lose.
Your just going to have to act "As If" up to the point of the D being final and beyond. It sucks, but wallowing in self pity and anger will not let you and the kids move on. She may regret this in the future after it is all done, but it is not your concern.