My girlfriend's best friend absolutely HATES me and wants to break us up. What do I do?

Anonymous
I've been going out with my girlfriend for about 7 months now. We met about a year ago. We get along great and everything is perfect except her best friend absolutely hates me and now I think she's trying to break us up. She's been telling my girlfriend lies about me that I'm worried my girlfriend might believe because they've known each other all their lives and trust each other.

Guys: What do I do in this situation? Do I just let what's going to happen happen? Or do I try to fight it somehow?

Girls: What would you do if you were in my girlfriends situation? If your best friend was telling you bad things about your boyfriend and your boyfriend was denying them and you had nothing to go on but their word and nobody else other than your best friend had anything bad to say about him?
My girlfriend's best friend absolutely HATES me and wants to break us up. What do I do?
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