Hardly universal. Polygamy, for instance has been practiced in many cultures throughout the course of history. Yet another reason that government should not be involved in such things; these are private matters, and governemnt has no place in determining them.
It's universally hetrosexual and outside of Africa it's restricted to one woman.
"Yet another reason that government should not be involved in such things"
You haven't given a reason. Govm't is involved to recognize and protect rights. If you don't want govm't involved, then don't ask them to get married. Tthose that wish to be called married will get the license and be officially recognized as such.
You are perfectly free to call and have any relationship you want with whatever sex, species, or thing you want, but no one and no arm of the govm't will recognize the relationship as a marriage. It is a rights violation to coerce others into conforming to, or accepting that as marriage.