When they find out about the separation they are going to want some details about what happened.
So they want details. Why do they want details? How will that improve things for you or your X or kids?
Usually when someone asks me a personal question I do not wish to answer or divilge information I respond with a more personal question directed for them. If they are stupid enough to answer your question they are too stupid for your personal details. Otherwise it's none of their business.
He who asks the questions directs the conversation.
"All I want is a weeks pay for a day's work" Steve Martin