Millie(let)

you'd def be valid calling yourself(yourselves?) plural, like, the way u described your experience is def more than enough to like, justify using the label for u

That absolutely seems to describe plurality, since even if they're not out most of the time, they seem to be other self-aware entities that exist in your brain, which would make you plural. :3

And the fact that you've experienced not-fronting basically confirms it~