Are humans really capable of such a thing as "Free Love"? That is, are most humans capable of having sex with someone without eventually developing attachments, jealousies, possessiveness, desires to bond with just one partner, etc.... Does Free Love work in practice?
If its a one night stand, its possible. But if the sex is continual, my assumption is that attachments will inevitably form.
Sex releases the neurotransmitter oxytocin, which correlates to feelings of deep union, from what I remember.
Staring into someones eyes also has the capacity of creating intimate feelings. People do this in speed dating. Staring into someone's eyes before, during, and after sex will help elicit some sort of bond. (Don't try and stare into someone's eyes in public. They will think your are creepy).
Romantic bonds also form between people that don't know each other very well, or see each other that much. Conversely, familiarity and habituation makes it difficult to form romantic feelings.
So, trying to have continuous sex with no attachments creates a situation that is ripe for romantic love and attachment to suddenly stir. Memories with the sex friend may eventually intrude one's unconscious mind--where hidden passions and instincts reside.