voices a "defense mechanism" to help me deal with people?

A little background info on me. I was diagnosed bipolar with obsessive compulsive tendencies eight years ago (14 years old). I did a few months on risperdal and was the equivelent of a laying zombie (walking being too much work). I told my psych at the time I wanted to try therapy unmedicated for a while and was immediately dropped as a patient. I continued on with life as if the diagnosis hadn't happened but was definitely hearing voices, this didn't bother me too much as I knew hearing words and random stuff was symptomatic of bipolar or demonic possesion (I used to be religious). The issue came a year after I graduated high school, I wasn't hearing random voices, I was hearing one person.

He had a name, Maverick. He was extremely opinionated about how I should handle situations over how I was handling them and over time he became a lot more developed. Now I should be a little more specific, when I say opinionated on how I should handle situations I mean that I was an extremely shy teenager, I had very few friends growing up and let a lot of people push me around. Maverick had a much more cool yet sharp attitude, always knew how to respond to somebody whether I liked the person or didn't. Now this almost sounds like a normal building of confidence except for it was a whole separate train of thought. It's really hard to describe and he and I used to have really long conversations over everything, almost like an invisible best friend.

There was an issue with control, days where I felt that I wasn't completely in control, there the whole time but almost a spectator. This worried me as I myself saw only two possibilities, schizophrenia or MPD. Not knowing enough about either I went to a new psychiatrist. We discussed my bipolar diagnosis and he felt it was accurate based of my moods of constant mania followed by short depressions. We discussed Maverick and he said it sounded like a defense mechanism to help me deal with people (My "defense mechanism" had an opinion on that, but it wasn't at all nice). He wrote me a script for lithium which I took for about a month, but the voice in my head just got louder and my energy dropped severly (I've been manic since 14 so balancing for me feels like a constant depression). I stopped taking the lithium, stopped visiting the psych and used willpower to try and force Maverick back. This has worked on and off for about three years.

I'm not really looking for a diagnosis, I think "defense mechanism" is understating the issue a little (or a lot). Things are pretty quiet in my head this last year or so and I'm just wondering if anyone else has had an experience this extreme caused by bipolar? I don't imagine mine is done completely, partially because I don't really enjoy the quiet, I had a lot of time to get used to having someone to talk to on the inside. I'm just trying to study what's going on and have a starting point to organize my thoughts on the situation, so any thoughts or experiences are very welcome.

Thanks!