Just to clarify OP, are you mainly interested in the aforementioned unravelling to happen mainly during the sex, or also in other aspects and/or during the aftermath?

... Also, how much violence and/or pain are you into? I certainly can do things with this, but I have very uh... esoteric kinks and am also a crazy slow writer. (Which is to say, really, really, really slow, so if anybody else wants to have at this, have at it :D!)