This idea of soulmates sharing souls is thought to originate from ancient spiritual belief systems that involve the concept of the soul being divided into parts. Each part searching for its other half, much like in the Greek Myth of Aristophanes in which souls split into two and spend their life searching to find their other half.
The concept of soulmates sharing souls is more of a spiritual or metaphysical concept, rather than a literal one. It reflects the deep bond and connection that some people believe exists between soulmates. This belief is not widely accepted and is based on personal interpretation and cultural and spiritual beliefs.
In more recent times, belief in soulmates sharing souls is also often associated with certain new age spiritual belief systems and practices. Books, movies, and other forms of popular media have also helped to popularize the idea of soulmates sharing souls.
However, it is important to note that the idea is not a scientifically proven and again, it is based on personal interpretation and cultural and spiritual beliefs.