If you're selling something with less than 5k words, I won't even consider looking at it. You are much better off at at least 10k words. If it's watered down or amazon friendly, you also aren't looking too good.
Amazing read. You have a real way with writing. I would have actually given 4.5 if given the option as the end of the story seemed a little cut off, but more importantly, I think it would have been most fitting if Alex had gotten her to beg him to be the only one to cum in her in front of them all as the ultimate humiliation and complete her inner turmoil.