having relationship with your friends brother

I was invited to a party by my friends and we were having a really great time and I met a guy who was amazing and really great to talk to and we totally hit it off but later I found out he's one of my best friends little brother and I talked to her about it and she was so excited that we were talking and was all about us getting into a relationship which I'm thankful for cuz this guy is really great but the only thing I'm worried about is is me and him don't work out what will happen to mine and my best friends relationship 😔😕