I already have a story for this, though the kid is a girl and the imaginary friend is trying to pursue a romantic relationship (despite the feelings being one-sided/the fact that's impossible.) <<that sounds so sweet!
Characteristics of Narcissistic Mothers by The Harpy's Child.also applies to siblings, partners. So sad! Many times if you know an abusive manipulator and cannot understand why they are that way - they are an extreme narcissist. Explains a lot!