I am single with no kids. Some of my friends are single and with no kids as well, but a few of them have children and are in happy relationships.
My friends who have kids become different since becoming parents. All they can talk about is their kids (or most they can talk about). Like there is nothing more in the world, no politics, no books, no movies, no nothing. It is like they don't have a mind of their own anymore. The child has taken over their souls.
I know that it can happen. Kids are the most important thing. But I hope it will never happen to me (if I ever have children). Hope I will remain a separate identity.