Well a really huge article by Michael Winn but a fairly huge topic...
http://www.healingdao.com/healinglove.html#sltAn interesting point made is that whilst our Shen (spirit) is gender neutral our bodies are not. He believes this leads to the phenomenon of all these Indian gurus going off the rails:
"The Polarity between Shen/Spirit and Sex/Jing
Because what happens if we try to get to a higher level of internal practice and we haven't dealt with our sexual energy? Our sexual identity issues will hang on us like a huge subconscious weight. Our unresolved sexuality becomes a kind of conscious darkness which is working as resistance against our attempt to restore spiritual neutrality, detachment or an inner sense of peace. You have this unresolved sexual desire running about in the subconscious, trying to complete itself by creating a viable destiny in the physical world.
So this is why so many very high, powerful, spiritual teachers came from a celibate life in India and they suddenly found themselves having groupie type of sex with dozens of their students. I’ve documented this on the articles page of my website, its called the “Quest for Spiritual Orgasm”. It goes into the distinction between the quest for enlightenment and the quest for immortality. The latter involves transmuting your sexual substance. "
another snip:
"The Spiritual Purpose Behind Every Relationship
That's the hidden purpose of any long-term commitment – to help each other grow their original nature. It's really a spiritual purpose, even though people ostensibly stay together for all kinds of reasons: economic, social, personal fear of change, for the kids, or just out of habit. There are all kinds of reasons why people believe they stay together, but underneath it is a deeper reason. The spiritual reason would be because we can continue creating something together through this interaction of yin and yang energies, creating an equilibrium in which yuan chi can manifest....
Why is Original Breath so important? Because its restoration completes the very purpose of human incarnation – the task of cultivating the original self within the physical plane. This original energy field, the neutral force holding the center between male and female, between yang and yin, is basically a love child. Yuan chi is the aspect of the Life Force that holds the quality of unconditional acceptance. Call it Divine Love if you prefer; but it does not imply a need for any action to prove its worth. Yuan chi is the “is”, the matrix, the primal stuff birthing our bodies and the body of Nature.
Yuan chi, Original Breath, is a state of being, or rather the dynamic aspect of the ground of being. It manifests strongly whenever you have sex or exchange your essence in other ways with another being. It's not male or female love. It’s not "I love you because you do this for me" type of reciprocal love. That is still polarized, basically an emotional exchange. We won't call that love - we'll say it's a balancing act of the emotions.
Whenever a couple begins to fuse identities, something from our androgynous pre-natal self forms. Some people form it instantly, other cultivate it slowly over decades. This original essence, once formed here in the physical plane, stays here. Whenever we grow our original essence, it serves the Tao by helping Tao to complete itself. Sexual qigong is designed to accelerate and intensify that process.
Because what happened to the Original Spirit is that it lost or scattered some of the neutral force – its Original Breath or yuan chi - in the physical plane in the initial act of birthing itself here. This loss occurred at the moment of the splitting of yin-yang into male and female bodies. The restoration of that original yin-yang harmony within its original matrix of yuan chi is the greatest “te”, or virtue of the Way. We could say it is the Original Virtue that precedes all other virtues."