SPOILER!
It boils down to having to trust what your lover tells you, really, and that is what both of them learned: Lauren, needing to realize that if he is uncomfortable he has to say so, and Simon to admit his willingness to make adjustments when things go awry. Or at least, that is how I see it. I think the issue of sexual boundaries in intimate relationships is too seldom explored, especially when it comes to expanding beyond vanilla play, and too often we see the extremes of abuse and breakdown without seeing how people might actually work to resolve them because they love and care about each other. And of course, also how members of a social community affect individuals and couple relationships by sharing (and interfering) based upon their own experiences. Wayne, of course, wants everyone to try everything, because he has and does, with tragic results. The "grapevine" and social pressure, and assumptions about what constitutes right and good behavior can also lead couples to trip up with each other, and why shouldn't this be covered in a story? Which is why I "went there."
Thanks for the comments!