it’s actually more than that.
marriage is a religious union designed for the benefit of children.
http://www.vatican.va/archive/ccc_css/archive/catechism/p2s2c3a7.htm
no secular institution has the true authority to perform a marriage. no homosexual relationship fulfills the requirements/purpose of marriage.
Are you suggesting that I am not married because my wife and I were married by a judge rather than a priest?