Not getting married is not the same as staying single. Relating to that not getting married part.
For example, we have already laws about "open marriage", as so many have family (kids, etc.) without formalizing their relationship. But their situation is not de facto really any different, and thus we have somewhat similar laws for them than for married couples. The thresholds are more like having kids, and or the duration of relationship/ living together, than the day when they were married (as they haven't got married).
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