I think there is a difference between multiple personalities, as in distinct separate individuals acting within one body and mind and different emotional behavioral personas, different facets of one person.

I think most of us will behave (have a different persona) at work vs. on a date, vs. with our therapist vs. with our families. At work one is professional, one doesn't show their emotions, or at least tries to suppress them, on a date one might be charming, inquisitive, happy, with our therapist we may feel safe enough to share most of our dark secrets, with our family we may love them, or stay away from them, etc.

When I go out to dinner by myself and I want a table vs a bar I joke with the hostess that I need a table for two, for me and my imaginary friend. This behavior is mostly for me because a part of me feels ashamed that I don't have anyone to go out to dinner and I'm afraid people will pity me. My imaginary friend is part of my behavior, part of my persona in situations where I don't feel confident enough to stand on my own two feet. I would never say she is a separate entity from me because she isn't.

Hope I made some sense.