Not much, actually. According to the strict letter of the law, an unmarried couple is not supposed to touch, let alone have sex. Living together is even farther beyond those boundaries.
Are these rules an anachronism? Or are they somehow sustainable? Or are they actually beneficial?
Well, considering the blog here, Judaism votes for option three. First, let's look at the statistics. Up to 50% of general marriages end in divorce. In the Orthodox commutnity, where these rules are observed by significantly more people, the rate may be as high as 10%. And that is considered an epidemic by rabbis. It is.
At any rate, the first thing we notice is that liberal dating values are no guarantee of marital happiness. Indeed, I believe they can be blamed for a lot of these problems. This is for a few reasons.
Firstly, the emphasis on sex takes the emphasis off relationship. Once the physical boundary has been crossed, everything else gets more complicated. A physical dependency can blind the couple to serious compatibility issues. What's more, if the prime interest is in sex, the couple won't put in the work needed to grow a spiritual relationship.
Living together, while it may SEEM like a good idea, is actually destructive to marriage success prospects. Instead of it being a time to "see if we get along," it is all too often an excuse for not making a commitment of marriage. There is usually a reason for not wanting to make the marriage commitment and live together instead. Well, whatever it is, that reason is not going away by itself. Living together for years and then marrying out of inertia is not going to change a basic compatibility problem.
There is also the assumption that you need to know as much as possible about living with the other person before committing. Well, in the real world, that's simply impossible. You can never know enough about your partner, and whatever you know will change with time and circumstances anyway. I know lots of people who tried it, and their eventual marriages crashed and burned terribly. It simply does not work.
Why is the Jewish way, while less "exciting and fun", more enduring and healthy?
Firstly, it puts the emphasis on the spiritual relationship. If the couple can't touch, they must get to know each other on a human level. That gives them a great, objective, start.
Then, if they do feel an urge for physical contact, the discipline of subjugating it FOR A TIME keeps that aspect of their lives in proportion. They put God and responsibility first, over sexual gratification. Their main interest is a spiritual life and home, not their personal physical pleasure.
That perspective is the cornerstone of successful marriages. Even within marriage, there is a time period every month when the couple refrains from sex. This renews the spiritual friendship that empowers their marriage.
The Talmud says that if God is present in the lives of a couple, there will be the glow of Divine presence in their home. If not, it will be consumed by fire. Keeping God present means observing God's standards and placing spirituality first.
Which, by the way, makes the physical relationship really intense and beautiful. Absolutely nothing is sacrificed in this regard. Spiritual connection, perspective and commitment make for the most fulfilling life relationship, in all its aspects.