It doesn't really matter how conservative a society is about sex and prostitution, it's still going to happen in bountiful amounts and fashions.
Not to criticize your critic, but I think the fellow might have a bit of naiveté about the reality of coital relations *throughout* the ages. Greater societal attitudes aside, sex happens. Kind of a lot.
Unless this brand of historical fiction requires a writing style synonymous with the period, that kind of complaint is a little silly.