Tell me if this is familiar.
You've got a friend. You get along fabulously. One day, a woman appears in the periphery of his life, hanging around just a little more than she should, trying to get his attention in any way she can. She's needy. Compared to your friend, she's wholly unremarkable. You might even feel a little sorry for her. Then one day, they're dating. Okay, fine. You welcome her. And then bit by tiny bit, you watch the man who was your friend be chipped away. I'm not talking about normal new-relationship triangulation, where this new influence causes your friend to change and evolve. That's natural and healthy. No, I'm talking about a descent into a sort of madness, where the whispers in his ear become his unquestioned perception of reality. Suddenly, you and your friend have conflicts. You question yourself but find that his other relationships are weirding out, too. He's suddenly secretive. He's distrustful of your motives, and he's not the least bit inhibited about telling you what you're really thinking—which often is shockingly far from anything that's ever crossed your mind. He's uninterested in hearing your thoughts; he already knows them. He does not allow his certainty to be diminished by data. You don't know for sure where this weirdness came from, but you strongly suspect. "This is between you two," the woman makes sure to say about each of his suffering relationships. "It has nothing to do with me." Yet his every question feels like an errand, and his every e-mail seems vetted. The new unease in your friendship breeds more unease, and you grow farther apart. You find yourself not really knowing this person anymore, nor caring to. And then one day your friend is gone entirely, and you just shrug. I've had two such friends, both male, both gone. The women whispering in their ears? Still there, still whispering. I call them "Yokos."
At first I thought Yoko unique to the first friendship, but then Yoko II appeared, so now I wonder how common it really is, and whether this happens with the genders reversed. Do tell.