That first ending you mentioned--revealing some secret that throws the rest of the story into a new light--is what's known as an "O. Henry ending", because that was the writer O. Henry's specialty: that surprise juke at the end, like the punchline of a joke. A lot of short story writers now assume that a story has to have that kind of ending to be considered good, but that's not the case.

The situation you describe, where there's a rape or abduction or some wild sex that turns out to be not what it seems, is so common in porn as to be pretty much of a cliche--that "Oh, it was her husband all the time!" business--and, like you say, that kind of ending gives the story a satusfying feel, but it ultimately defuses or destroys a lot of the erotic heat as we find out that what we thought was happening wasn't ot at all: it was just two lovebirds playing around.

The alternative is to go with the story as written and let the sex act itself serve as the dramatic bones of the tale. That takes more courage on the author's part, but it's ultimately more honest too, I think, and it makes the sex hotter. Since most people are here for the sex and not the literary value, I'd stick with what you have and forget the surprise O. Henry ending. Let the sex speak for itself.

My opinion only, of course.