First two paragraphs seem reasonable. To the third though:

I think I've mentioned this before, but I find Ridley Scott's portrayal of Future Christians in the film Prometheus interesting. The space ship's archaeologist character, Elizabeth Shaw (played by Swedish actress Noomi Rapace), wears a cross and professes christian beliefs at a time when christianity has apparently gone into decline and christians have become relatively uncommon. Yet as a single christian woman she has a sexual relationship with a man on the ship, which suggests that christian sexual morality during that religion's long twilight will tend to converge with secular moral views.

Many, many self-identified Christians from pretty much all denominations have premarital sex. See e.g. here. And this isn't a new thing, even among the Puritans this was not uncommon (in there care we can tell based on extremely short times between many marriages and when children had their births recorded).