What does it mean if no one can tell my ex and I are separated/broken up?

My ex (30M) and I (29F) have been broken up and separated for over 2 years now... we currently coparent 2 young children and still see each other on a regular basis. We both attend our childrens' extracurricular sports & classes, school events, and go out "as a family" from time to time. I understand that people have different coparenting relationships but for us, whenever we meet new people or other parents, they are always shocked to find out my ex and I aren't together. What does this mean and why is that? Him and I do not partake in any form of physical contact.
What does it mean if no one can tell my ex and I are separated/broken up?
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