"Will they get their happily ever after? Or will it blow up in their faces? " - I mean...If you listen to the people steering you towards sharing your wife, what would you expect but for it to blow up in your face?!?
The movie "The Sex Monster (1999)" got it pretty much right, except the ending. No, it's not porn. It's a lame raunchy comedy.
Now, I'm sure we're going to have plenty of fans on here arguing with the usual " yea, but if there's trust and mutual respect ...". You can have that with a coworker. Or a roommate. If you want your marriage to last, you need love and intimacy. And there is no intimacy involving three, four, five,or god knows how many more people into your relationship. As for love...The more you share, the less you get. Obviously.
You literally train yourself with every action. From breathing to walking to the food you eat and the genres you like. " It's an acquired taste". If you become numb to the idea of your partner having other partners, can you really expect a happy ending?