Considering how much they'd been drinking, I'm not surprised they had the idea to have a threesome. Especially since the mom is such a badass. Kissing your daughter in front of her boyfriend meant offering yourself up as a pussy for copulation. And the guy took advantage of that offer by banging both of them. He even shared his sperm with his mother when he came between his girlfriend's legs. Damn, that's fair!
The mother has been waiting for this event for a long time. For her son it is not only a graduation, but also a ticket to adulthood. So the mother decided to give her son the basics of science, which he would need in high school, so he would not feel like a virgin and a loser.
And the lady's very experienced, I see. She fucks with pleasure, her anus is clearly developed and she is used to sucking dick. An early young woman and as they say without complexes. I wonder why she does not fuck her daddy, he could give her more money for sex. Or does he have no energy left after the same temperamental mother? Either way, it's interesting.