I would definitely consider divination for this situation. If you do not know how to read for yourself, then find a talented one. Everyone's response here will be pure guess, albeit some may be "educated" guesses. My educated guess would be that this individual was a soul mate. Contrary to popular "new age" belief, we can have many soul mates. Mates can be friends, not just lovers. When I was young, I was personally taught that they were called "kindred spirits". I think it's a more fitting name.
The other possibility would be what is known as a twin flame. It goes along with the Greek philosophy that we are only one half of a whole soul. We can only have one twin flame. But they don't mirror us, they are just like us. This causes conflict because who can really live with themselves? I believe I would drive myself insane! They are intensely drawn to one another because like attracts like, so you attracts the other half of you. They aren't necessarily meant to be together. And most of the time, one is a spirit and guides the other.