I really liked this one. It had an in-depth meaning beyond simply. short sentences and I always love that in a story.
Your character is telling me this story, as if she/he is recalling it, and I like that. It's intruiging that I'm not being shown something, but it's as if she sat down and told me, "This is what happened."
Imaginary friends are always a great thing to use, because they're a big part of childhood. Everyone had an Imaginary Friend. It was very good how you described the kinds of things she and her Imaginary Friend. I loved the swing set/ swee-saw thing. Obviously, a child can push themself on the swing, but they can't do a see-saw by themself. It was cute how you morphed that into her interpretation of what he was doing with her.
The saving the worl thing was very realistic. Any child would hope to assume that everyone is doing something goof, and the way you add "I was foolish," makes me think that now she understands the bad things of the world, leading me to believe this is told as a flash back.
Of course little kids are curious about swears, and you have the Imaginary friend swearing. It made sense.
The very ending made me think. Your Imaginary Friend was stubborn and mature. When you say that "he was everywhere," are you referring to how, when a child grows up, they suddenly realize how mature everyone is beginning to get? How they start swearing and the like? The character may be understanding now that life repeats itself in the strangest of ways, and reminds you of things that may be long forgotten. At least, that's what I got from this.
Great write. I really enjoyed it.
(PS. I noticed you mentioned your own name and said it was partially autobiographical or something. If I insulted you by saying "the character" I apologize.)