In the Tao of love, you find very similar ideas to those you find in tantric sex.
These two streams are definitely connected and when we track them back, I am sure that we could find a common source.
Tao of Love and Tantric sex are like parallel lines of evolution which aim at the same goal.
I am convinced that some ancient medieval rituals were very similar in concept as what you have in tantric sex.
If we dive into native traditions, I am sure we would as well unveil similar ideas.
One idea, many streams leading to the same place.