The ability of people to freely associate with one another should never be regulated.
It is not any of the governments business who I chose to associate with. Nor is it yours. So then, why is it any of the governments business who I chose to live with? What if I chose to live with them forever?
Some people do not like that two or more persons of the same sex might be allowed to have the same tax advantages, survivorship rights, or the right to buy insurance as two or more persons of different sex. Why should the sex of those persons matter with regard to taxes or insurance?
The government not only has no business changing the tax or insurance rules when people are of a particular sex, but it also has no business telling us what we can name our unions or bonds. If we want to call it partnership, or marriage, or whatever, it is our right. It does not harm anyone else if your neighbor says he is married, or if he says he is not. The government should not dictate the terms of civil contracts. This includes any civil contracts that two parties make when they form their associations. Government has a place in enforcing contracts but it already does that for contracts that are constructed by the interested parties.
The government also has no business issuing 'licenses' to marry. That arcane requirement first started to prevent or control persons of different races from marrying. It's time we end that barbaric practice and start recognizing the freedom of the people to associate with whomever they please, free from extra burdensome regulations regarding taxes or what name they choose to call their union.
Marriages or unions are between the parties involved, and optionally between them and their deity. The only time government should get involved is when the parties have breached their contracts and can no longer agree on the terms of dissolution. When that happens, recourse/relief is provided for in the civil court system.