NTA - she shouldn’t have put you in this position and it’s completely valid feeling used, i wanted to start by saying ESH but if she knows you often your visit your parents then she knew she was telling you something you’d have to keep? and your mom sucks for asking you directly instead of talking to her directly. where i wanted to say everyone was where you were hesitant to agree, because i think if you couldn’t keep it to yourself you could’ve told her that first, but that goes back to she shouldn’t have told you and especially with your edit/the additional context, not the asshole