What do I do?

This guy that used to really like my bff was talking to me the other day and he was talking about how she apparently “ghosted him” (not true) and he’s like “yeah, I had to like tell myself to stop liking her. I was like why do I even like her she’s flat.”(also not true) And I feel like my bff liked him back but just never admitted it out loud. So I’m confused on if I tell my bff about that conversation or not. I think that if I tell her it will make her insecure and I don’t want that to happen, but I don’t want her thinking he’s an innocent/good guy. (cause she might secretly like him. I DONT KNOW WHAT TO DO!!!!! HELP ME PLEASE?!???!!!