i think cohabitating is actually more of a commitment than marriage itself. yes, you heard me right!
think about it, either one of you can walk away without the hassle (binds/ties/legalities). the fact that you are "together" in spirit and not legal, indicates that you are together for the right reasons, of your own free will, and NOT because you HAVE to be together due the contract of marriage and all of the BS that goes with canceling that contract.
without the contract of marriage, the balance of power is equal. either one of you can walk away, and both of you know it.
marriage is a legal contract and nothing more. with it, the balance of power can, and often does, take a nasty turn. neither one of you can walk away (easily), and both of you know it. this tends to breed resentment over time.
recently a buddy and me were at a bar. he glanced over at a nice looking, tight, 25ish blonde, and he said to me, "damn, that's what my wife looked like when we first got married". he's about the same in looks and body. she fell apart, and he didn't. he could nab that same 25 year old blonde right now and he knows it. that little hampster wheel in his head is starting to spin. nevermind the fact that his wife nags the fvck out of him. she nags because she CAN! THEY'RE MARRIED! IT'S HER GOD-GIVEN RIGHT!
people tend to think about divorcing their spouse for quite a while--years perhaps. once they make the decision, tack on another year, two, three, or more just to get it done. hopefully, you won't get too screwed.
for people who have been cohabitating for a while, then get married, they do have higher divorce rates. most likely this is because they've been living together, de facto "married" already for several years, and the conclusion is almost always, "might as well get married". the reality of it is that they were probably ready for a "divorce" anyway. then they get married, then they get divorced.