availability of the opposite sex, ect.
Assuming heteronormativity here, are we? :)
:)
Not really, since in the time span in question I can't think of a time where access to other people of the same sex was made purposefully difficult because of their sex. Segregation by sex has however been a norm in many different times and places (its with us even today whenever you go to perform your bodily functions in a public restroom).
There was a historical shift in beliefs.
I find this very odd. How could a major cultural lineage be wrong about something so much a part of ordinary experience?
When I say wrong, I don't necessarily mean that we're right, or the ancients were right, though there's a lot of evidence that the Victorians were wrong.
My favorite theory is that people's amount of desire for sex varies sufficiently that there's enough noise to make it easy to see patterns that aren't there. I leave the possibility open that there was a change (possibly dietary) which affected libido levels differently between men and women.
People are sufficiently punitive about sex that there's going to be lies and misdirection to support the current theory about how people are supposed to be.