What are the meanings of marriage? Why are some couples together for 10, 15+ years without marrying?

What are the meanings of a marriage to you? If you're married, do you think of it the same as way you did before marrying?

Why are some couples together for many years (10+, 15+) years without marrying?

Do you think it would make sense to want a marriage, but not building a family / having kids? Meaning do you think there's a point in marriage if a couple doesn't want to have kids?
What are the meanings of marriage? Why are some couples together for 10, 15+ years without marrying?
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