Once you notice how someone talks about people behind their back, you can’t unhear it.

Some information cannot be put back. Hearing how somebody talks about an absent friend tells you the rule rather than the exception, and from then on you are in the room with the knowledge that your turn exists, whatever they say to your face. That is not paranoia, it is just arithmetic.

What you do with it is yours to choose, and the useful part is not punishment but calibration: tell that person less. Then turn it around, because this is the week’s harder question. Nobody is entirely clean on this, and the fix is to stop once rather than to decide you are different.