[Nifster]

I see no where in the constitution that marriage of any kind is addressed

[Blood of Tyrants]

Up until about the 1860s, marriage was a religious ceremony with the justice of the peace performing non-religious ceremonies. There was no marriage license.

However, when my great-grandfather was married, he had to post a $2500 surety bond that he would have to surrender if he divorced. That was 1906.

[Theoria]

It doesn't have to be, you are free to enter into any contract that doesn't deprive life and liberty of another. It is up to government to honor that contract. You were already born with numerous rights not listed on a piece of paper.