A promise to keep a secret can conflict with a responsibility the promise never anticipated.

A promise is made inside the situation as it was understood at the time. Circumstances can change so that keeping it means allowing a harm nobody had in view when the words were spoken, and then loyalty and responsibility pull in opposite directions with no clean way through. The conflict is real and treating it as a simple matter of keeping your word is a way of avoiding it.

If you find yourself here, go back to the person you promised before you go anywhere else. Tell them what you are facing and what you think you have to do. It may not resolve it, and it is the difference between a hard decision made honestly and a betrayal.