I genuinely held up my big sister's relationship as the example of how monogamy could work between people for decades since she's been with her boyfriend since HS and now she's forty. Turns out almost the entire time they were swingers and her boyfriend fucked dudes. She confessed to me last year. She also has a girlfriend on the side.

It's none of my business but I've legit never looked at her the same way since and just kinda avoid her. I don't know if I'm in the right or not.