When the 'best friend' doesn't like you

What do you do when the guy you're crushing on has a girl 'best friend' that doesn't like you ? He hasn't said anything about it but i as a female am hostile about a girl being a guys 'best friends' because I know girls who are 'best friends' with the guy and they're really a side piece and being a cancer I could be over thinking the whole thing but I just want some input on what to do. She hasn't said anything to me since She found out I liked him and now she's always mugging me and if I'm around with my friends while she's talking to them she keeps the conversation with them. I feel like my presence offends her royally but ??‍♀️ What should I do.

I don't think a female friend is automatically a side piece...that's absurd

But I do think female friends tend to be possessive...regardless of the lack of romantic interest they are used to being the main female in their friend's life and don't like when another female comes along and takes their attention.

Also they are typically overly critical of their friend's girlfriends in my experience...trying to find reasons not to like her instead of the other way around