any time after 6 months of dating . Yes live together before marriage, I firmly believe it's a good thing to live with your "potental" to see just what they are like when they let their hair down and relax in a home sitation.
I lived with both my wives before I married them.
If he waited on me to marry we would never live together
It's really up to the couple.
I never though I would wait until marriage to begin with.
My personal experience is that I lived with my boyfriend extremely early in our relationship. I was new to his town, I had to stay at his place before I could move into my own...and never leaved him but that's just how life went