This is from a site on Ascended Master teachings, though I overall thing their teachings are misleading.
However, I think they have a good understanding of this concept.
via (
http://www.summitlighthouse.org/soulmates-and-twin-flames/)
Soulmates and Twin FlamesTwin flames, soulmates and karmic relationships are all on a quest for love and a perfect relationship – a quest for wholeness.
Soulmates and twin flames, spiritual relationshipsThere are three types of romantic relationships that help lead one to this wholeness: twin flames, soul mates and karmic relationships.
Twin FlamesTwin flames were created together in the beginning and share a unique destiny. Created in a single fiery ovoid, they were separated into two spheres of being—one in a masculine polarity and the other in a feminine polarity—but each with the same pattern of divine identity. Though they spend some lifetimes together and others apart, their tie is eternal, and after they have each united with their Higher Self they will ascend and be together forever. But not all the beautiful and soul fulfilling loves are those of twin flames.
Soul MatesA soul mate tie is different from that of the twin flame. Whereas we each have only one twin flame, we can have many soulmates.
“Soul mates share a common mission and comparable stage of spiritual development. They come together because they are working on the same type of karma and the same chakra simultaneously.
So soul mates have an attraction that is based on the sacred labor and on the path of self-mastery.
A soul mate is like the echo of oneself in Matter working at the same task to fulfill a blueprint for God.” – Elizabeth Clare Prophet
These spiritual relationships tend to be harmonious and satisfying, and such kindred souls can accomplish great things together.
Karmic RelationshipThen there is the karmic relationship where two individuals are drawn together for the balancing of mutual karma. The karmic tie may be the tightest of all and begin with the strongest attraction. This is because the soul has a deep yearning to be free, and has an inner knowing that this connection is a key to resolution through balancing karma that is often harsh, such as violence, hatred, abandonment or even murder.
AlonenessFrom time to time, there is a feeling of emptiness, a loneliness that reveals the inadequacy of a relationship based solely on karma. Yet though they are frequently difficult, these relationships are important in achieving self-mastery on the spiritual path.
Love is the KeyEveryone experiences all three types of relationships over the course of their lifetimes. The key to wholeness in all of these spiritual relationships is to love every soul.