What secret do you know that could ruin someone else's life?
Probably a boring answer but I know my grandmother's credit card information. I live with and help take care of her, so she doesn't mind sharing it with me. Not like I'm planning to do anything nefarious, but I guess technically it could ruin her financially.
There's a teacher at my kid's school that I fucked multiple times a few years before I got married. She was married at the time, though I didn't know it.
I have pictures, and videos. Not just ones with me, she kept such things with other lovers as well. She showed them to me by sending them to me. I have permission to have kept them,
though I had forgotten about them until my kid started high school and I ran into her.
Now, her husband is fine with it, they're open. He was kinda surprised when I quit having sex with her when I found out she was married (I just don't like complications, even with mostly casual sex and minimum complications).
But if it got out at the school, or to the school board? It would be a huge problem. Our town isn't totally backwards, but it isn't exactly a hotbed of open minds either.
There's no way in hell I'd ever say anything to anyone where it could be found out, and I sure as hell wouldn't break trust and show anyone the files. But I've been debating erasing those files just to be sure. They're on a drive that isn't connected to anything, which is why I haven't already; I'd have to dig the thing out and hook it up.
Even if her husband was OK with it, she still should have told you she was married. The fact that she didn't would be enough to make me end it. I mean, if they have an open marriage, why avoid mentioning it?
She said that she didn't think it would be a regular thing, and by the time she realized we were good enough together sexually to keep at it, she just forgot to mention it for a while.
Which, I could see that being a realistic occurrence. We didn't exactly talk much when we would meet up.