I don't think people should live together before they get married. Yes, my first reason is because of my faith, but after that comes a slew of statistics about why living together before marriage really isn't the great idea we're lead to believe it is.
A recent example from my life: I've been staying with various friends since I had a bed bug scare, and one of them told me the futon on her porch was already made up because a friend had gone through a bad breakup and needed a place to stay. I found out that I knew this friend, and it's the sort of thing where they really should have broken up a few years ago, but it wasn't financially possible because at the time one of them was a freelancer and wasn't making a lot of money. She stayed in a relationship largely because she couldn't move out.
People will make whatever choices they want, and that's their right. Someone I care a lot about recently made the decision to move in with the significant other, and I'm not happy about it. I still love that person and won't behave any differently, but it makes me sad that people don't know the facts. Moving in will not fix a relationship. It won't change the problems. And the statistics show that it's not beneficial in the long run (higher chance of domestic abuse, less satisfaction sexually, among other things).
Maybe you're not religious at all. I don't expect the fact that it's not God's ideal to mean anything to you if you don't follow God. I would just say to do some research. Check out some studies and educate yourself. Popular society (media, especially) is wrong.
(I'm not looking at any stats as I write this, but I've seen them footnoted in a book I read recently. If you're interested in more info, I can dig out the book and look up the info.)