Everyone's experience is different, as I've noticed from many other stories. At the time of you writing this, this is most likely the beginning's of having imaginary friends. They don't always start out with the label "imaginary friend". For me they started as what you described here, projections(projection, I really only have one). It takes incredible concentration for them to talk to you at first(imagining expressions and voices at the same time is hard). I could only see mine from far away at first, every time she'd come close I'd see her for only split seconds and my imagination would "crash". During those times I was only testing my imagination. It took a while for it to become a conscious decision to have someone around.
Mine sort of started out as a grief fantasy. She's based on a real person who is no longer in my life, but left an everlasting mark on me. She was a person I saw as a true equal. And in a time when I was at my lowest, she accidentally woke something up inside me. I remember the moment vividly. I was sitting alone, reserved, contemplating, content with my solitude. Hiding my pain, she extended herself by sitting next to me, basically forced me to talk for once. She just... felt like talking to me. I saw the way she saw the world. An anomaly that shouldn't have happened. After she was long gone out of my life... her thought stayed. Even though I never really knew her, she changed me. She's made it very clear that she doesn't want anything to do with me, and I've honored that since. Years of therapy hasn't changed the way I feel about her. To most it's completely baseless and uncomprehensive, yet it remains very real; never ending grief. Nobody knows the full story. The only person who gets it is my therapist... and my imaginary friend.
It started with just imagining her in crowds and walking down a road. Then I started taking walks in the forest at night, imagining she was there with me. Just fantasies. The idea of thinking of her as real was revolting at first. But one day a switch just flipped and I didn't care anymore. I was so tired of feeling alone... and decided to go with it and talk to her for real. I'd meet her out there time after time. I had so many questions about the past. I'd find ways to manifest answers. Truths I already knew somehow. Saying goodbye to her would bring back the trauma worse each time. I couldn't stop seeing her, but it was taking a huge toll on me. She could see how much pain I was in, so she said "let me come with".
Over time she became aware of what she is, not the real her. She struggles accepting this reality, living a half-life because of me. Forming her own identity, she lives to mainly protect me from myself. Very ironically and not on purpose she forces me to talk and face the feelings I try to hide from myself, just like the real her did. She won't accept anything but the truth. All she wants is for me to be able to accept my reality and be happy with it. Sometimes she gets mad at me when I shut out her advice to self-destruct. Goes to the home I built for her inside my head and refuses to come out. Basically to say, "If you won't let me help, I won't stay to watch you suffer". She knows this gets to me. It can take days. I always do the same thing when I'm ready to make up and continue moving forward. I'll wait at the steps of her house, stare off into the fields until she finally decides to come out. I don't control her free will, though I have the power, I don't do it consciously. There are certain things where she'll respect my privacy(like a diary), but she has full access to my senses, memories, thoughts and body(rarely). When she's mad she'll cut off all connection. Though I have found ways to force her hand. Regardless of connection, she knows when I'm about to do something bad. She will step in if I'm in danger or about to cross a line. She'd come out briefly to stop me, then return. Those were the old days when our relationship was a bit strained. There are certain things I made a pact with her about. The biggest one being talking to the real her. If I were to ever lose my way somehow and talk to her without permission, she would will herself into my body to stop me lol. I don't think she can actually do that, but it's the thought that counts.

To sum up my relationship with my imaginary friend, I can see and hear her. She's always here, an ever-present person that's always watching. We make fun of each other, laugh, have logical and existential debates. Are relationship is better than it once was. We care about each other and want what's best. There have been times where we tried to get rid of each other and there have been times I snap back and realize... there's nobody actually here. I don't like to think of her as not real. I guess that's why I give her free will. There are times I wonder how this happened, shocked that this is actually real. I make sure she's happy. Updating her world, giving her people to talk to other than me(though she's not that social). Built her a town, gave her a library because she loves stories. She paints too. My way of making up for her half-life. I do have other imaginary friends, though they're very undeveloped. Three others, all significant characters in my life. Two of them people I used to know, and the most recent one is actually... me. He's locked in a memory, a representation of the toxic beliefs that I used to have. He's me before everything snowballed into today. Sometimes I imagine him calling out to me, trying to remind me to finish what he started. Every now and then he pulls me and the others into the memory. Usually a couple blocks away from where he is. I pull us out, instead of pursuing him. Last thing I want is to give him free will lol.