Long time friend, not so much a friend anymore...

Hello world, I need some advice. This is my first time here, so I apologize in advance if this is incorrect in anyway. I have had my closest friend in my life for 10 years or so. She has crossed me one too many times ( now dating my brother-slept with him 2 days after she moved home from getting divorced) anyways, I am not engaging in the friendship. I don't ask her to hang out, we don't talk, we don't text. I see her around the house (because she's seeing my brother) and I am pleasant. She recently went on a trip and bought me a gift, it was a friendship necklace (btw- we are grown ass adults) and I accepted it because I didn't know what it was until I opened it in front of her. I am not one for confrontation...I avoid it like the plague. But, I need to be honest and tell her that we are just not good friends anymore. However, her and my brother are pretty immature and I have a feeling this will cause a bit of rift in the home and relationships with both her and my brother. How the hell do I tell her that I don't consider a good friend anymore without her or my brother totally losing their shit? I don't want her to have this false impression of a friendship that is purely one sided. Any help is appreciated.

In my opinion I would let the friendship fizzle out, if she is more interested in your brother then she won't really see much of a difference. I understand this situation as my sister's partner was my boss and he fired me for a really silly reason but I didn't react. Sometimes the best action is nothing.

No words required. My advice would be just to keep to yourself like you have been, and let your actions affirm that there is nothing left. I think if you were to try to verbalize what you're thinking - it would turn ugly, there would likely be a confrontation by her and/or your brother. The best thing to do, is to just keep your distance.