At our present level of evolution for society as a whole, the need and desire for both sexes is self evident. There is no doubt that many people feel the ultimate happiness can be found in such relationships.
However, for starseeds that have incarnated here for the purpose of helping the planet, many will tend to prefer to be alone and not take a chance in getting caught in the karma of relationships and to focus on their mission. Also with spiritual development, the happiness that one can get with such relationship can be evolved to one that is based on the relationship with life in its larger context where there is an awareness of interaction with all of life. The relationship may not be as intense, but the duration is much longer, essentially being always present; it is one where you are never alone and happiness and contentment is always there,not dependent on another being.
One example of a whole society existing at this level would be a race of hermaphrodites. This would only be possible when the beings evolve to a point where they control their DNA since the imperfection of our DNAs is a prime reason for co-creation with 2 sexes. Here is an e-book on such an evolved ET society:
http://books.google.ca/books?id=MCuM...bnail#PPA27,M1