Together, divorced, or just plain didn't work out life still happens. Some things you can control, and other things that are completely out of you control.
If something has to change because it is out of everyone's control then be adults and make it work.
If something has to change that is in control of everyone then be adults and figure it out. As long as it is planned well in advance.
The only people that lose in this are the children.
So here's a thought grow up and behave like adults so you children are never forced to choose.