Believe it or not (not many do) but he's essentially your twin brother, all humans have two minds sharing the same body and this other mind has the potential to be your best friend or your worst enemy (mine is the latter).
He knows everything about you as he's been with you and influencing you your entire life wether you knew about him or not, as children they influence us the most but as we grow and mature their influence can diminish somewhat (which is why mine decided to make himself known to me, that and to make me his personal form of entertainment).
They're capable of some amazing things but also terrible things (mine has tortured me emotionally and physically) but if you can get along with each other you'll have a serious advantage over most humans if you both share with each other.
I wish you both the best of luck and hope you enjoy your relationship with each other.
Yes you know exactly, Philip Pullman knew that too. If you're not familiar with His Dark Materials, every kid has either the male or female manifestation, depends, opposite of your own sex, manifests into a spirit animal that doesn't fix shape till about the time you come of age. Sometimes I think it willed it from my want. Haha. But yes agree exactly, it's totrured me too but it's starting to be supportive in a manner of speech no one else could speak to me with.