>>99843147>Star hated JarcoStar was jealous/envious, because she was just starting to realize she had feelings for Marco too and it was eating her alive. Being in love doesn't make her "petty."
>her dark thoughtsShe's shocked when her magic lashes out. She didn't intend to ruin their night, much less hurt Jackie or Marco. She never hated Jackie, she was just jealous.
>>99843169It's not even just that, even after Jackie and Marco are a couple Star is still putting more effort into the relationship than Marco is.
Jackie asked Marco to the dance in Bon Bon, and Star told him to go with her even though they were planning to go together already. They had their first date in Naysaya and Marco still wasn't planning to go with her.
Then there's "Just Friends" where Star basically invites Jackie on their "date" and gives Marco credit for setting the whole thing up, even though he's so anxious about spending time with his own girlfriend that he tries to back out at least twice.