The wonderfully hilarious thing about this is THAT THERE IS NO BIBLICAL DEFINITION OF MARRIAGE! And - even better - in the Old Testament, a man could have multiple wives.
And isn't the point of the New Testament that it rendered the Old Testament obsolete? Isn't that changing the laws of God?
But if you think not, then well -- as for those immutable laws - spend a little time with Leviticus and tell me how you feel about that.
Meanwhile, marriage is between one man, one woman, plus possibly her sister, and for sure his brother's widow, should such an opportunity arise.
Conservatives have no sense of irony, but I am forever wedded to mine.