Now add some details to your situation.
so one of my best friends just told me she likes this guy who's my best guy friend's best bro (and he's super short ! but thats not important ;)). she told me and another besty not to tell ANYONE ! i said of corse i won't. but now everytime i hang out with my bgf and he brings up something about his best bro i have an erge just to tell him because i know we'd have a good laugh and i tell him a lot. i know i shouldn't because he will obviuosly tell his best bro no matter what. plus i'll be breaking my promise. but i tell him EVERYTHING. you don't need to tell me not to tell him. its just how do i keep it from him ?!?