i shouldn't tell him , i know. but then again . . . i HAVE to ! :(

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 ?!?