How would you all handle this?

I just had a situation where my cousins girlfriend overheard me having a convo with my cousin about a job her girlfriend and I both work at. I haven’t received some parts of a deal in over a month and was thinking about leaving if adjustments can’t be made. The girlfriend over heard the convo and went back to our boss to give her a heads up I may resign.
Mind you this girlfriend years ago did something so bad I wasn’t speaking to her. What she did wasn’t toward me but it showed her character. Few years later I began to give her the benefit of the doubt and became cordial with her had she seemed to have worked through whatever.
Now she does this and lied and said she never told our boss that. Meanwhile I only told my cousin of the situation. & my boss said she told her🤦‍♀️

How would you all handle this?
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