Back in the 70's, I read a book about alien life forms that had an unusual ability. The aliens in their natural form were shapeless protoplasm, but when they came into contact with a human being they eventually took the physical form of the person whom that person loved the most. For example, if a man were grieving over his absent "true love", the alien would become a duplicate of this woman. In the book, a man who was a narcissist used one the aliens to create a duplicate of himself (he loved himself more than anyone else). I believe the novel explored the implications of being able to "be with" someone you loved even in their absence and maybe against their wishes. And also the implications of manifested self-love. Not sure of the details. It's been a long time since I read it. Can anyone help?