My experience is living together is only playing at the relationship. It is like someone saying "I love you for the moment. If things get tough I am out of here. Only committed superficially. I am not all in and it really doesn't matter if you are not all in."

You can live with someone everything seems hunky-dory; and then marry and the dynamic will change; sometimes for the good and sometimes for the bad. My experience was the person thought it meant possession he could drop the phony act he had been fronting; which to me was a significant demotion and ended the relationship; thankfully without a lot of drama but it was not painless.