Correlation does not equal causation. This is an oft quoted meaningless statistic, high on the list of meaningless statistics.
It's true, perhaps that more people who never live together, never have sex until the wedding night, have fewer divorces. But it's not because virgin wedding nights have some special magical affect on the length of marriage, it's because the kind of people who tend to believe in waiting till marriage also is comprised 100% of people who take marriage vows very seriously, usually for religious reasons.
On the other hand, the type of people who will live together before marriage will comprise people who are all over the board in how seriously they take marriage. Some will think it's OK to leave when they get bored, or have an affair, some will take it very seriously, as least as seriously as the chaste group.
So it's not the shacking up first that leads to divorce, it's the tendency of that pool of people to include those who divorce for lesser reasons.
Living together before marriage does not lessen the commitment of those who believe in commitment. Nor would not living together first increase the commitment of people who don't believe in commitment.
One thing I personally believe to be very important is that something substantial should change when a couple gets married. Since I also happen to believe that there is no justification for pregnancy outside of marriage, it should be obvious what one logical change should be.
Note that this does not imply that couples should not cohabitate if they could do so without intercourse. I find it somewhat interesting that cohabitation is viewed as equivalent to intercourse when there are probably more people engaged in promiscuous sex who don't live together than who do.
However there is some evidence that the experience of cohabitation itself tend to "train" the partners in the practice of shielding themselves from real open-hearted emotional intimacy and making only provisional commitment.
Which is, come to think of it, an oxymoron.
I myself would argue that living-together involves a kind of falsehood. The experience of intercourse speaks a language in the flesh which says "Now I belong to you." Even women who think of themselves as somewhat un-tender, emotionally, can be quite surprised to find themselves reacting to sexual union this way.(And yes, guys, too: but I suspect that women are quicker and more sensitive this way.)
So your actions say "we mate; we're mated; we belong to each other" in the deep language of the body; but the terms of your cohabitation give the lie to that.