Hi Reddit. I (24F) need your judgment.

My ex-boyfriend (27M) and I are still on friendly terms. Back when we were together, I met one of his close friends and that guy’s then-girlfriend. I never really had a friendship with her—we just met a few times at gatherings. She always seemed like a nice person.

Fast forward to now: that friend is engaged to the same girl… but I know for a fact that he cheated on her with her best friend while they were still dating. The affair is over now, but the worst part? That best friend is still in her life and is now one of her bridesmaids.

It makes me sick to see the bride-to-be posting all happily on social media, while this woman who betrayed her is smiling by her side, acting supportive and leaving fake nice comments. I feel so uncomfortable just knowing all this and staying silent. I wasn’t super close to her, but I can’t help but feel like I’m complicit by doing nothing.

My ex (who lived with his friend at the time) even confirmed that the girl used to sleep over, and it was obvious what was going on. So I know this happened.

I don’t want to ruin someone’s wedding or life, but I also hate the idea of this poor girl marrying someone who was unfaithful—and still keeps her backstabbing best friend around.

Would I be the asshole if I sent her an anonymous message just saying to be careful who she trusts? Or should I stay out of it completely?