Trevor-Jill Relationship

Trevor Sheldon and Jill Roberts were in love until Trevor cheated on her. Trevor cheated on Jill with someone. In the deleted scenes of the film, it is heavily implied to be Jenny Randall, hence why she was targeted.

However, the official cut of the film ignores this (likely as it would more obviously implicate Jill to being a suspect). Trevor continues to pursue her even when Jill resents him for his actions.

Other aspects of deleted scenes explain Trevor's personality more obviously, to show he is not the culprit, and is genuine in trying to repair things with his ex-girlfriend.

Scream 4
Trevor wanted Jill back and went after her, calling her. He followed her and came into her house without permission climbing through her window (like Billy once did for Sidney). He also told Kirby and Olivia Morris to tell Jill to talk with him. In the climax, he is captured by Charlie. Jill, who is revealed to be Ghostface along with Charlie, shoots Trevor in the crotch then in the head, obviously killing him. (The murder was reciprocal to the original. Jill shooting his groin is reciprocal to Sidney's "reverse intercourse" move done on Billy where Sidney stuck her finger in Billy Loomis's wound from the umbrella in the original. Sidney and Jill, both, shoot their former boyfriends in the head.)

Jill and Charlie wanted to frame him to be The New Billy Loomis for her Remake of The Woodsboro Murders. She wanted to be the new Sidney; the sole survivor so she could become famous and become the new Sidney Prescott and Randy Meeks. But it ultimately failed when Jill betrayed and killed Charlie and Sidney, Judy, Gale, and Dewey told everyone the truth that Jill tricked them and they believed them and she officially became the new generation's Billy Loomis and Trevor officially the new generation's Neil Prescott.

Script
Jill was based on Billy Loomis and Trevor was based on Neil Prescott. While Billy was the killer and Sidney was the survivor in Scream, Jill was the killer and Trevor was the innocent victim who was framed and killed in Scream 4. His role ultimately became hybrid of Billy's character, Sidney's victim status, and Neil Prescott's circumstances of being framed.

Trivia

 * Jenny asks if it is Trevor on the other line when ghostface calls her further revealing they have some kind of a relationship. Subsequently, it is Jill that attacks her as ghostface and kills her due to causing Trevor to be infidel to her.
 * Olivia openly states she can't stand Jenny Randall referring to her as "the other woman" due to her knowing she was with Jill when she slept with Trevor. She appears to be on neutral terms with Trevor, however.
 * Kirby is distant with Trevor after he cheated on Jill. She will be openly rude to him, and not invite him to her house with the rest of the gang. She will be sassy in shunning him in favor of Jill.
 * In an unedited scene, later deleted, Olivia openly calls Jenny Randall "the other woman" due to her knowing she was with Jill when she slept with Trevor.
 * Robbie taunts Trevor due to his suffering after Jill found out he cheated; however, they are cordial with each other.
 * Charlie dislikes Trevor, but says things and acts passive aggression towards him in commentary. Furthermore, he dislikes how he won't leave Jill alone as that he is now her girlfriend in secret.

Behind the Scenes

 * Jill Roberts is portrayed by Emma Roberts.
 * Trevor Sheldon is portrayed by Nico Tortorella.
 * Emma Roberts, Nico Tortorella and Rory Culkin all starred in the movie, Twelve.