Consent is certainly important, but they don't need your consent if the image was obtained legally and thus subject to fair use, or if you gave them permission in the past.
That’s why it’s not illegal to call someone a slut (even though that also damages reputation)
It can be, if that constitutes defamation or libel. A passing statement wouldn't, but a post on a popular website absolutely could. It all comes down to the damages that (false) statement caused.
What if the recording was made without the person’s consent. Say someone records their one night stand without the other person’s knowledge but they don’t share it with anyone. Should that be illegal?
That depends on whether there was a reasonable expectation of privacy. If it's in public, there's no reasonable expectation of privacy.
In general, I'd say intimacy likely occurs somewhere with a reasonable expectation of privacy, at which point it would come down to consent (whether implied or explicit).