I can see your point about long drawn out divorces and I think that the reason God is keen on commitment is for our protection, not to get our hearts stompped on, and not to tie us into unhappy long term relationships.
I think it's important to step back for a moment and look at what marriage actually is.
Marriage is an entirely human invention. It doesn't occur anywhere else in the animal kingdom. Sure, you have animals who mate for life (and others who don't!) but that's all to do with evolved survival techniques. You'll find that animals who pair up for ever will tend to share the care for their offspring which is clearly beneficial.
Marriage though, is a tool of law. It binds two people legally. This brings benefits within human society. But it's also a tool of security. The perception is that if some agrees to marry you, they are committed to the relationship. The perception comes from two angles, one is the vows which you take to commit to the your partner (though in the end, these are merely words and anyone can say them as part of a ceremony whether they mean it or not) and the other is that legally it's a PITA to separate from marriage so why would anyone bother marrying if they intended to end it.
That is a very cynical view of marriage, granted, and it's far from the commitment I made to my wife, but that's a very personal commitment which one makes to oneself.
So honestly, I don't see that marriage itself has any bearing on the success of a relationship, if you are genuinely committed to each other then your relationship will flourish, if you are not, then it probably won't. As such, I don't treat marriage as anything particularly special to my relationship. Not that it didn't mean anything to me to marry my wife, it did. But if we hadn't, I wouldn't feel any differently about her. It's a social statement to marry and carries some legal benefits. But to suggest that it would be wrong to live with someone or to sleep with them before you marry, to me makes no sense whatsoever.