Paris finds out that not only does Tristan not want to date her again, even though their evening together seemed to go fairly well, but that it was Rory’s idea that he ask her out. She immediately throws a fit, accusing Rory of giving Paris her “cast offs”, so she’s obviously been quite aware of Tristan’s attraction to Rory.
Whenever Paris and Rory seemed to be becoming friends, something would happen to ruin it. Of course Rory could never do anything to hurt Paris, and would instantly forgive her whenever she hurt Rory, so the only way it could happen was for Paris to behave in a completely insane way, where she got angry over almost nothing, and would hold a grudge about it for an inordinate time.
The Annotated Gilmore Girls 