Marriage was instituted by God in the Bible. Homosexuality is condemned in the same Bible. Why do you think you need have the blessing of God and the church on something that goes against what they both stand for? Go ahead and do what you want, just don't expect to have the blessings of those who disagree with the whole concept.
I don't usually post to these threads but this statement caught my eye.
Do you really believe that pre-Christian (or pre-Abrahamic) societies had no such thing as marriage?
I myself was married in a civil ceremony. Does this not count in your eyes?