I messed up

my best friend had issues with her boyfriend and she told me something and i was so mad at him that i told our other friend asked her not to mention it and try to knock some sense into him ( me , my bff , boyfriend, other friends , other friend fiancé are all one friend group) she slipped and told him in the middle of them fighting and he got mad at his girlfriend I’m so scared of my friend finding this out and she will never trust me again and i cant afford losing her it was the one time i have told anyone anything and it had to have this big effect our other friend swore to me on her dad grave she will never tell him or her but im still worried what can i do

-confronting my bff is not an option -