I agree that government should have no role in determining who should marry whom:
No law prohibiting mixed race marriages.
No law prohibiting mixed religions from marrying.
No law prohibiting same sex couples from marrying.
Only logical, therefore, that the number partners to a marriage is not the business of government. Logically, under all the aforegoing, one man could marry several women. Add one or two men to the menagerie if he desired. Similarly, one woman must be allowed to marry as many men as she chooses plus a few women if that floats her boat.
Once we put all that archaic stuff behind us we can move on to deal with situations like the teenage girls who just love their horses. And older couples who love their cats. Why should they be kept from fully embracing them?
Feel the LOVE!
And, of course, NO requirement that any of those marriages involve sexual intercourse. That, for many, is a small part (if any part at all) of marriage.