Yes I have long time ago when I was 17-ish Actually with one of my best friends her ex.
And she's still one of my closests friends.
Lovely story actually.
She knew about it before I wanted to tell her, it happened in the weekend because the guy couldn't keep it a secret to his friends and it got around on Monday back in school.
I told her I needed to speak with her urgently so we met up at her house... I was so nervous all afternoon and couldn't say anything until we were at the door me about to leave and said I need to get something off my chest.
Before I could say anything she grabbed my hand and said: "it's ok, I know. Say no more. I'm happy for you.", and the we hugged for a very long time before i left.
One of the best moments of my life with her. We still chat about it until this day.