It's a story, not an essay. Have the characters change as a result of the action, not as a result of what they say to each other or to themselves. Remember to describe the characters and the setting, because they are part of the story. Don't describe things that are not in the scene. For example, don't describe the color of something that neither or no character can see.
Pornography is a rigorous calling.
Do not be a smartass about the sex. That is not erotic. Write it as hot as you can. If you feel compelled to be cute, it is probably because you are embarrassed. If you don't see an ending, the story isn't over.