It's the love that survives anything and everything, that struggles and pulls through, that even when it seemed hopeless and out of control it still beat strongly. It's the love that is not superficial, a love that transcends not only the physical world but time itself. It's not perfect, but it's wonderful and still exhilarating after all those years. There are people who get married, then get divorced, but come back to one another *ten years later*. A love that isn't entirely human. It's the love that, if lost by a foil against destiny, will leave the people empty, pinning and never forgetting and never fulfilled. It's the love that makes you cringe at the thought that, had your life gone differently even for a millisecond, you may have not met this person - but in your heart you know you would have, some way, somehow, because soulmates always find one another.
You are both, in all the ways that matter, the same person. Once experiencing this epiphany, you will not only come to truly understand another's soul, but better understand your own as you are merely reflections of the same inner being.
We are imbued with unique qualities at birth/conception/creation that follow us and develop our whole lives, some inner resonance. And somewhere, throughout that life, if we're fortunate and have our eyes, ears (and hearts and minds) open, we'll come across someone who shimmers the same way we do and be elevated, forever changed.