It's about two sons taking care of their mom. Sorry, stepmom, must remember the current chicken-shit super-taboo. She has broken down after her husband died, and can't manage to do anything around the house, and the sons are tired of taking care of her (even though they live in her house for free).
So they tell her that she will be fucking them, or else they will leave her. So she does. It ends with both of them coming all over her face, and with the shot of her sad and broken face staring numbly into the distance, contemplating a future of being a sex-slave to her sons. You can actually see sperm dripping from her hair...