I'm going to be friendly to someone who hurt my best friend
Why would you be friendly to that person?
I just want everyone to be happy. But my friend could be hurt by it.
It's not nice to be friendly to someone that hurt your friend. You should just not even talk to this person.
Yay, I made my best friend super mad.
Well, it doesn't make sense to be nice to someone who hurt her. You didn't think that out very well did you? Apologize to your friend now and let by gones be by gones, and avoid getting her mad again.