Though I've never been in one, I think they can last for a certain amount of time, but the "long-term" situation must end at some point. It can't be permanent. I see it as sort of being in a relationship that's on ice. It's still there, and you can cultivate it to a certain extent, but you can only reap the full benefits if you're truly THERE for each other. You need to thaw out at some point. I'm sure some long term relationships have lasted years, but I think for many that's just too long. It would be like trying to survive on only tofu.