The presence of illegitimate children or the practice of premarital sex does not establish your argument of a cultural standard that a man slept with a woman for the purpose of determining her fertility before marriage. That is the claim which you have, so far, failed to establish.
Since you have stated that there is a “record of this sort of behavior”, I’m sure that the appropriate primary source(s) will soon be forthcoming.
Perhaps instead of assigning beliefs to other posters, you should back up your own beliefs with evidence, not assertions.
I think they were more concerned with not getting stuck with an infertile woman.