Um I NEED HELP:(

Umm... I didn't really get your question, but tell me if I'm wrong.

So your sister said something to you about your best friend. She keeps doing it and it annoys you. Now you've ended your friendship with your best friend because of that, and you want to know if you did the right thing?

So if that's the case, have you tried asking your sister why she lied about him? And I don't think you should end a friendship because of some lame gossip. And if you're doubting about the lies, have you asked his side of the story? With that he'll also know why you've ended the friendship (if he didn't know it yet).