If you want to get married, you do. If you don't want to get married, you don't.
High Priest Peter H. Gilmore wrote a Satanic wedding ceremony which is in his book The Satanic Scriptures which could be used for those who wish to do so. Other people might write and create their own ceremony.
"Spiral Out: a bleak, page-turning, unforgettable read. Existentialism at its most hardcore" - www.uvray.moonfruit.com