I saw an interview once with a man and his wife, and the man suffered from this delusion. It had been going on for a couple years, and he was undergoing therapy. The wife (who was thought of as merely a clone - not an alien) stayed with him despite the hardship. She seemed to think he would eventually come out of it. It was rather interesting because it apparantly happened to him overnight. He woke up one morning, and just assumed his wife had been replaced during the night. He didn't harbor thoughts of murder with her, but stopped all physical & sexual contact. I was amazed the wife was hanging in there. I wish I could remember the source, 20/20 or Oprah or some claptrap.