It was a pleasant surprise to find the complete text of this astonishing short story here, in an apparently authorized online edition. Even though you can read it all on screen, I recommend encountering it as a (physical) page-turner, as I did.
Banks does things with voice and point of view here that I hadn't even imagined as possibilities, and he creates two characters I won't forget anytime soon. This is indeed a love story, though saying so is a bit of a spoiler. Required reading for human beings who've fallen in love, plan to do so, or don't plan to do so.
Here's my favorite passage, and the engine for Banks's jaw-dropping journey:
"When you have never done a thing before and that thing is not simply and clearly right or wrong, you frequently do not know if it is a cruel thing, you just go ahead and do it, and maybe later you'll be able to determine whether you acted cruelly. That way you'll know if it was right or wrong of you to have done it in the first place."
You'll want a hard copy of this one. Click here for the Amazon link to the impeccable short story collection in which I found this masterpiece.