My friend M (F21) told me that recently she messed around (foreplay stuff) with a guy (23ish), and that he then got married the next day. I was disappointed in M for doing this, but then she sent me a picture of the guy and his new wife...

His wife is my old friend P(23) who I used to hangout with and date her brother. We aren’t in close contact anymore, it’s more of a social media friendship now as her brother and I aren’t together.

I know that telling P might ruin my friendship with M and it might not even be my place to tell. But my old friend P is a great person and I feel horrible. Do I tell my old friend P that her husband has been unfaithful, and if so, how?