My limited experience with such arrangements is limited to three couples, two of whom I've gotten to know fairly well, though I remain in touch with only one today.
That relationship is badly broken, and kids are involved. I'm also confident, admittedly with limited knowledge of the relationship, that its failure was not traceable to the lack of a marriage license provided by the State.
* * * *
Much ado about the trial run of an in-flight-assembled b0mB on Northwest Airlines 327. I reassert: we have to make Uncle Sugar recognize that airline passengers are not an asset to be secured, managed, and protected but an asset to be trained, prepared, and informed, and most of all permitted to protect air travel. The biggest obstacle in the way of us protecting ourselves aboard commercial air is Uncle Sugar. First he can get out of the way, next he can actually offer help.