It was around 130 years ago....that some mental-health doctors finally sat down and did some analysis over the problem of people having imaginary/invisible friends. From what is written of the era, there was a trend underway (various social circles)....where a phenomenon of social business was conducted. Meaning? Like-minded people gathered...sipped tea, coffee or wine, and talked about their 'friend' (the one that didn't really exist).
Some people would just go simple on this route....saying the non-existent friend was a ghost or some angel. As the decades passed....this went to a more science-fiction like creation....being aliens, robots or vampire-like creation.
I worked with a Air Force NCO who was a instructor at some AF school. He'd been forced into the instructor status (unhappily).
Before his Air Force years....he'd spent most of two years in New York City as a ambulance 'helper'. On slow days, he'd talk about the patients picked up (most all had psychological issues).
One day in the Air Force class...he had deal with a 19-year old female airman. Having failed a test, he was supposed to counsel her (basically to tell her to clean up her act) and review her notes. The notes were not that readable and had a lot of symbiology drawn out. Her response was that she could read them, and her friend 'Jessica'. Ok...he thought, and the counseling ended.
Later in the room....he noted that she sat in the far corner of the class....with a empty table next to her. He gazed at the class listing of students.....no 'Jessica'. Just on a hunch....he walked over and asked where 'Jessica' was and she pointed at the empty table. That was enough to set my associate off....running to the commander.
The base clinic took her in....spent two or three weeks making sure she wasn't dangerous, and then gave her papers for exiting the Air Force. They weren't going to keep her.
If she hadn't failed the test? Oh, I would imagine she would have gone onto 20 years of service....spending the whole 20 with 'Jessica' and be nearing 60 years old presently with her imaginary friend.
I'm not anti-imaginary friend....but I'm probably not pro-invisible friend. It's like some gal walking around and imagining that she has a horse tail, or has a body covered in non-existent tattoos, or that she has a imaginary 'male-'tool'.
When you suggest I need to cooperate with your friend's situation and just accept the invisible robot-friend or imaginary cowboy 'Lex'....I'd rather not play the game.