what do I do if my girl cheats on me with a famous guy and justifies it by saying that it was a “once-in-a-lifetime opportunity” and anyone would’ve done it?

I dunno… see, it’s all a matter of your dignity. And it’s 2021; you could be talking about some dipshit like Logan Paul.

If by “famous” you mean your girl tripped and fell on Alexander Skarsgard’s dick, your only question should be whether or not she stuck the landing. And your only response should be to never, ever let her forget she owes you a big one. Or a bunch of smaller ones. On her nineteen year old sister, three times. Whatever works for the two of you.

If, on the other hand, “famous” means she rimmed Danny Masterson in an IHOP toilet because he promised to introduce her to “Kelso and Jackie” and get her a free body-thetan checkup… dump her ass and move on. Cheating is one thing… bringing shame upon your household is another.