One of my favorite episodes of Fringe.

    PETER: Olivia? Are you okay? What is it?
    OLIVIA: You know what Barrett said? He said that he looked into her eyes, and he knew that it wasn’t her.
    PETER: Olivia…
    OLIVIA: I understand the facts. I know that she had reams of information about me and about my life and about the people that were close to me. And I understand that if she slipped up that she would have a completely reasonable explanation for it. And I guess to expect you to have seen past that is perhaps asking a little bit too much. But when I was over there, I thought about you. And you were just a figment of my imagination. But I held onto you, and it wasn’t reasonable, and it wasn’t logical, but I did it, so… why didn’t you? She wasn’t me. How could you not see that? Now she’s everywhere. She’s in my house, my job, my bed, and I don’t want to wear my clothes anymore, and I don’t want to live in my apartment, and I don’t want to be with you. She’s taken everything.
    PETER: I’m sorry.