The Open Marriage and Divorce: Can open marriages ever work?

OPEN MARRIAGES AND DIVORCE: I was browsing through the UK Guardian and there was an article about open marriages and I didn’t read the whole thing because I’m a bit too distracted to read due to a lot of issues going on at the moment, including but not limited to the Midterm Elections in the U.S., the fact that I can’t vote since I am thousands of miles away from New York where I am registered (but, I mean, who could I reasonably vote for? Nathan Deal? Roy Barnes? Their politics is a bit too dirty for my taste), the infestation of hole-digging gophers in our garden and trying to figure out how to get them to eat the “peanuts” we bought at Home Depot….my over-eating (I’m still subsisting on candy left over from Halloween; I wouldn’t be surprised if a grew a few cavities), the book I am working on tentatively called Dennis, and any number of other variables….but it did strike me this phrase in the Guardian article, “the open marriage.”

I never understood what that meant. What the heck is an “open marriage” anyways? I remember years ago this married guy was hitting on my like there was no tomorrow. At the time I had not ever been hit on by a married man before and it was shocking to me, I didn’t know what to make of it. Finally, I said to him, “do you have an open marriage or something?” In my delusions, I really thought that if a married man was that open about his desires for another woman, he wife must have given him permission to do it. I couldn’t fathom that a man in a marriage (or even a serious relationship with another woman) could seriously be so barefaced as to hit on another woman unless he had the permission of his wife. I know. Hilarious. I know. Trust me, I’ve grown up. And I know better. There is a name for these miscreants. It’s called YOU ARE A FUCKING CHEAT! A used car bleeping salesman! Get outta here! 
But at the time I was like, “do you have an open marriage? I don’t understand? What do you mean that I am hot?” And I really expected a frank explanation. It wasn’t a rhetorical question. I was serious.  Sometimes my cluelessness is more than embarrassing. It’s downright dangerous. Man.
So now, years later, I am sitting here wondering, well, what exactly is an open marriage? And do people actually give their spouses permission to cheat and have relationships with other people? And why? How does that help their marriage?
I think the concept of an “open marriage” is an oxymoron. There’s no such thing. If a spouse is giving another spouse permission to cheat, the marriage is over and one or both of them don’t want to admit it. There’s no need to be married in order to have an open relationship. That is what single-hood is for. When you are single, you can have as many or as few (as in zero) sex partners as you want. When you are married, that’s it. It is just you and the spouse. Any marital arrangement that involves permission to have other partners is a cry for divorce. It really is. It’s a farce.  A mockery. A misdemeanor. A nonentity. A lie. A deception. IMHO.
I mean, what do you think? Can a couple really have an open marriage that lasts? Or is it always a precursor to divorce?