Aristotle talked of the philosophy of friendship. How a friend is basically another "self" - a real friend would keep you grounded. This is because we choose our friends based on their similarities to ourselves. They keep us in check. For the two of us, it's clear that we are the same person split as two separate entities. We're angsty and smart and very politically aware. We even dress similarly. We might think the same things at the same time. We talk similarly. As a matter of fact, many people think we must be related just because we're so similar in so many aspects.
Perhaps that's just the kind of friendship that some people need. You don't need to grab a mic and tell the whole world that this is your best friend, that you've been friends for the last 5000 years. Some people don't need to be loud about it. Sometimes there is just the silent acceptance of what was meant to be. And I believe that we were meant to be close. I believe fate caused us to cross paths. And maybe we don't need a title. Just the acknowledgement of the link between our minds is enough. We help each other anytime the other needs it. We are each others shoulder to cry on, audience to rant to, and the first person either of us will call with good news. I am her, and she is me.