One of the more interesting concepts I've come across in sci-fi books are the alternate ways they've come up with handling marriage. I wonder if online there's actually a list of the possibilities people have come up with...

One I did like the concept of is having a 'short-term' marriage that only lasted a year, which, at the end of the year, could optionally be upped into a 'contractual' marriage that was effectively the same as a current marriage. If the couple chose not to continue the marriage instead, no one batted an eye.

I have a feeling that if something like this was actually used, there would be an increase in short-term marriage and a marked decrease in long-term marriage. I've lost track of how many marriages (including my sister's) lasted less than a year because one of the parties of the marriage (in my sister's case, her husband) was for one reason or another unready for marriage, but did it anyway.

That's hardly science-fictional. It's a Beltaine tradition, and also possible in Islam.