No marriage should be “legal.”

I support marriage equality. Adults who love each other and want to commit their lives to each other in the form of a marriage should be able to make such a commitment. All adults should be able to publicly celebrate their love. Marriage, however, should have nothing to do with legality.
Where does it say in the Constitution that the government should decide what kind of marriage is okay and what isn’t? Isn’t marriage a cultural or religious institution? Or, rather, marriage should be a cultural and/or religious institution.
I suspect marriage fell under government regulation when laws were required to control men’s property (a wife and her property)…? I haven’t researched the history of it, but that strikes me as likely.
The government should have no say in what counts as a marriage.
I support marriage equality.