The problem for those who assert biblical authority in support of traditional definitions of marriage is that one could with equal validity assert that the lending of money or certain kinds of haircuts are forbidden by God or that slavery and the subjugation of women are authorized by the Lord.
Some of the worst mistakes of my life have been haircuts.
Remember the first time you went to a show and saw your favorite band. You wore their shirt and sang every word. You didn't know anything about scene politics haircuts or what was cool. All you knew was that this music made you feel different from anyone you shared a locker with. Someone finally understood you. This is what music is about.
Think back to yourself at age 18. I know I was mighty different than the Patti I am today. As we grow up we grow out of our haircuts our apartments and - often times - our romantic decisions.