Is it usual to split up when marriage is mentioned?

What I mean is you meet someone when you're in your early 20s probably sexual attraction

Then when you're say 26 you think.. Do I want to spend the rest of my life with this person? Do I want to make children with them?

Then maybe you split up and look for someone with those marriage qualities? Parent qualities?

Or is that just very mean thing to do and mean way to look at life?
Is it usual to split up when marriage is mentioned?
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