It sounds like you did great, Thumper. Yes, it is very sad for your kids, but they (once again) get to see you modeling consistent and rational behavior in the face of the opposite from your ex. That is very important. Also, as much as we want to protect our children from sadness and disappointment, we can only do so much because those things are inherent in life. Facing them with a supportive and emotionally intelligent adult to guide them through can build both character and compassion.
All that being said, I do feel your pain, and hope it passes soon!