So let's say he found a whore and agreed to fuck her for money. Who doesn't, but why doesn't he protect himself? No matter how many times you explain to people the dangers of unprotected sex with a casual partner, they go at it again! Personally I always have condoms with me, women often have them too if they like sex!
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!