Well, it's clear you have a vision for the world and an aesthetic for the kind of sexual activity you want to depict; that's all good. You're chapters have a good amount of length and detail to them, and you don't shy away from sex, which is no doubt a plus for many readers. As a nitpick, your story is described as being in the 3rd person but you're actually using 1st person throughout ("I..." "My..." etc.)
At the moment the story is strictly linear - nothing wrong with that, however if you do plan on adding any branches later, it might be helpful to change the default "What's Next?" question to something a little more tailored as to how the story might zig instead of zag, so to speak.
As far as suggestions for improving your writing, my main suggestion would be to use your character's names more often! When you have two women having sex in particular, "she" and "her" can get a little confusing as to how they're used. This is especially the case when you have long stretches of dialogue without any distinction between who is speaking.
Also, and this is a minor gripe, it feels weird that you use "O" instead of "orgasm." If you're going for something specific with that terminology, no need to change anything, but you might want to play around a little more with the terminology for anatomy - it doesn't always have to be "pussy," it can also be vagina, slit, quim, gash, cunny, cunt, fuckhole, etc. Again, your particular aesthetic might call for a specific terminology, but a little bit of variation can help keep the text from growing stale.