Um I NEED HELP:(

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

So your sister sagte something to Du 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 Du want to know if Du did the right thing?

So if that's the case, have Du tried asking your sister why she lied about him? And I don't think Du should end a friendship because of some lame gossip. And if you're doubting about the lies, have Du 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).