My best friend thinks a "guardian angel" saved her from her cheating ex. It was just me being a coward.

Three years ago at a house party my best friend's then-boyfriend left his phone face up on the kitchen counter while he went outside to smoke. The screen lit up with a tinder notification previewing a message from some girl named Chloe saying "cant wait for tonight :)" Instead of being an adult and telling my best friend to her face, my brain completely short-circuited. I knew if I told her directly, he would twist it, claim I was trying to sabotage them, and she might hate me for snooping. So I took a photo of his screen, went to teh public library the next morning, printed it out on a piece of paper, and slipped it into an envelope under her apartment door with no name on it. She dumped him that exact afternoon. It’s been three years and she still regularly talks about the "anonymous angel" who saved her from wasting her twenties on that loser. Every time our friend group gets together for drinks, she brings up this mysterious stranger who watched out for her, and I just sit there sipping my cider pretending I have zero idea who it was. I took the cowardly way out because I was scared of confrontation and she turned me into a folk hero.