Definitely not true. I know of many happily married people in the lifestyle. It really depends on how solid your relationship was to begin with, and how much communication and trust you have with your partner. Some people see it as a bandaid to fix what is already broken—which just delays the inevitable. However, if you have a strong relationship to begin with, and can love multiple people, or just want to screw around with multiple people, it can be an amazing and wonderful thing.