I think my friend likes my crush...What do I do?

So lately my not so close of a friend has been flirting with my crush, giving him nicknames, always picking and joking around, etc. I used to think he was starting to like me back but now that she has came into the picture, I'm not so sure anymore. It seems like if her constant flirting continues he will start liking her back. My friend and I aren't close at all and barely talk. Any advice?
I think my friend likes my crush...What do I do?
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