Except she doesn't just cheat on you. She goes out and finds some street thugs from the projects, and she lets them gang-bang her. She even lets them nail her in the ass. She never lets you nail her in the ass. And she lets them videotape it. And then she swaps out your DVD of Ghostbusters with the DVD of her getting fucked six ways from Sunday, and just when you're expecting to see Peter Venkman, you're looking at your girlfriend with a dick in her ass and a nutsack in her mouth.
You sound like the voice of experience here. The whole nutsack in her ass stuff is standard venting, but no one would make up having Ghostbusters swapped out for an amateur smutfest.