I don't want to get into a discussion about not marrying the person in the first place, that's obvious. I want to know legally want could happen if you get married but don't actually return the signed marriage certificate to get filed? Could your 'spouse' still get her name changed to yours? If you split up, would you still be liable for alimony? Would you still have to split your stuff? Could you get in trouble for not turning in the certificate? Etc.