I write, so talking to myself is tax deductable. To write I have to see how GI Joe or Barbie would respond to the same situation, and then how they would argue about what it means.
A book with only one charecter, and that perfectly normal, would not sell. Look at Shakespear, his charecters talk to themselves at length, and it is the best part.
Any one thing can become tiring, Humans are endless, so ramble. This can cause headaches.
Try writing it as dialog. mental stuff, great ideas, fade like dreams, and keep coming back, bad writing hangs around. Writing gives a visual subject to revision. I was a great ranter and had nothing to show for it, the same for great thinkers, who never express it. Bad writing is real, and can be improved.
We are more objective about our written word. We keep the good stuff and sweep the rest under the rug.
My advice to writers is write, burn it, write some more, burn it, for our heads are full of garbage, and what is good, is the current stuff, deleating files is good for the hard drive. As long as it is in there, it is in there, once written, it is out and used.
When my head was full I could not fill a page. Once I got some out I could write several pages. When a hard drive fills up it has no blank spot to write to, so information processing slows to a crawl. Once old files are printed out and deleated, that open spot is available for processing. Then I can write many pages, for I have a empty field to pull them from the files and order them.
Thinking and writing are very different. I write it all, without thinking, it is an open relief valve. I write some real garbage that got stuck to another idea I was working. Let it out, for it can be deleated later. It cannot be if it is left in the head.
The inner dialog is almost gone now. I talk to myself still, but as a director, preparing the inner cast for application in written work. Science Fiction is excapest, murder mystries homicidal, and a lot of people write porn. Switching around gets more cobwebs out.
I wrote a lot of history, anthropology, as that is what I read. It was in there, I could remember it, but through writing my own ideas, linked works I had read, updated information, and turned all into one story, my understanding of thousands of books read. I could not do that inside, it had to come out.
It opens space, orders processing, and my thinking is current, not recycling disturbing thoughts from long ago over and over.
Hand flapping is aspie, throw in a keyboard and it is acceptable. Talking to yourself is called bad, writing to yourself is called art. It did work well for me.