I'm a Christian so as far as I am concerned God has dominion over Marriage. You are not married when you get a marriage license. You are not married when a preacher stands up and says "I now pronounce you man and wife." You are married when the Holy Spirit places the Fact that you are married on your heart.
There is no description of how to start a marriage in the Bible because people can't start a marriage.
God telling you that you are married isn't good enough for many people. It isn't that they don't believe in God, they typically just don't believe anyone who claims God told them something. As a result people have created a bunch of rules about marriage that have very little to do with God.
In the United States we have a civil union licensed by the government that we call "marriage". It really isn't marriage since God is not in control of it, but, for traditional reasons we call it marriage.
I have a friend who is gay and is a lawyer. He believes that gay couples can have the same rights married couple have by filing the necessary paperwork. I used to believe that. Over time I have realized that only a lawyer can file all the right paperwork and know the law well enough to stand up for the rights the filed paperwork gives a partner.
My cousin got married in San Francisco during the time gay marriage was legal. One simple license takes care of all the paperwork and reduces the legal rights confusion.
I think homosexuality is wrong under God's law, but, I don't think homosexuals are wrong. They are just people making what I think are poor decisions.
Does that mean they don't deserve the same rights I have? Should everyone I disagree with lose their rights?
Of course not. In fact I am often friends with people who disagree with me because I respect people who have strong, well thought out opinions.
Do I believe homosexuality is genetic? Not a frick'in chance. Darwin was an idiot who believed homosexuality is a generic response to any genetic defect. That is total crap. Homosexuality is a choice people make.
Homosexuality, like abortion, is a choice. They are choices I do not agree with.
God invented Choice. Who am I to deny anyone their right to invoke their God given right to choose?
Call it marriage or a civil union or whatever, just quit claiming that you are God and have dominion over the things of God.