What is...are...the biblical definitions of marriage?

Certain groups opposed to marriage equality will like to tell you that marriage is defined as one man and one woman. They are clearly missing out on how the men of God were told to view marriage.

Now clearly marriage has been redefined since the days of the bible and churches don't insist on parts of the law of Moses such as the rape victim having to marry her rapist. God chosen people and the line that bore Jesus were a line of polygamists and men with concubines.

Just saying. So why when they say that marriage is all about love and point to Leviticus as the reason that man and man can't be together and woman and woman can't be together that so often the marriage then is not about love. That the love often comes with a subsequent wife or concubine.