Let me tell you what my best friend says on Plato. First off, she is very much obsessed with the idea of soul mates. She believes everyone has one, and shall find them before their life is over. Whether they marry or not, they will still meet. They could meet on the subway, on the street, in the park, in a taxi...... anywhere.
Anyway, this is what she tells me Plato says about soul mates. I think it is very interesting.
A long time ago, there were these creatures, basically comprised of two human people. Their rulers were the gods above, and these creatures wanted to act and be just like the gods in every way. The closer they got to being godly, the more worried the gods became. They decided action was necessary to eliminate all chances of these creatures becoming godly.
So, the gods severed each creature into two halves, and threw them all over the world. Since these creatures were hermaphrodites, one half became male and the other half became female.
Occasionally, a creature would not be hermaphroditic; therefore, when split, two females or two males resulted. This is who Plato accounts for homosexual relationships. All of the hermaphroditic creatures enable heterosexual relationships. All of this is a part of nature, since long ago, both creatures were quite natural.
Anyway, as the gods split the creatures into two, they mixed the halves all up around the world. Some of the halves, now people, got scattered rather closely, which is why some people DO find their soul mate. Others got thrown half way around the world. So, some might not ever find their soul mates. This was the ultimate plan of the gods because without the other half, the creatures could not be totally happy or sufficient.