His jealousy could also show in his magic. Maybe he tries too hard to outperform Fleur in magic tasks or challenges. He might be constantly comparing himself to her and pushing himself to the limit just to prove that he is better, which is a sign of his jealousy.
One possible reason could be Fleur's unique charm. She is part - Veela, which gives her an alluring quality that might make Harry feel insecure. Another reason might be her skills. If in the fanfiction she is shown to be extremely talented in magic, especially in areas where Harry struggles, it could trigger his jealousy.
One possible reason could be that Harry admires Bill's adventurous past and Fleur's beauty. He might feel a bit envious because Bill has had these exciting experiences and Fleur seems so alluring. Also, Harry might be jealous of their relationship as he himself has had some difficulties in his own romantic pursuits.
He often shows it through his actions. For instance, he'll start growling at the person he's jealous of. If it's another male around Kagome, he'll give them a menacing look and might even bare his fangs a bit. His body language becomes very tense and aggressive.
Dean's jealousy might show in his relationships. He could be overly competitive with Harry, especially in areas like Quidditch or academic achievements. He might also try to steal the spotlight from Harry whenever he can in the fanfiction, by showing off his own skills or knowledge more than usual.
His jealousy might make him a bit withdrawn from Bill. He could be less friendly and more distant, which could cause some tension between them. As for his relationship with Fleur, he might act a bit awkward around her, not really knowing how to handle his feelings.
Another way is that Edward might isolate himself from Mike. He doesn't want to be around Mike because seeing him makes Edward feel inadequate. So he avoids situations where he has to interact with Mike, which shows his jealousy in a more withdrawn way.
Often, Ginny will try to insert herself between Harry and Hermione. She might constantly try to get Harry's attention when he's with Hermione or try to exclude Hermione from activities that involve Harry. In some fanfictions, Ginny might even spread rumors about Hermione to try and drive a wedge between her and Harry.
Often, she becomes overly possessive. If she sees Percy talking to another girl, she'll quickly insert herself into the conversation. She might put her arm around Percy or give the other girl a look that clearly says 'he's mine'. This possessiveness is a clear sign of her jealousy in the Percy Jackson fanfiction world.
Luke's jealousy of Percy in Percabeth fanfiction is manifested in various ways. One way is through his attitude. He may give Percy cold looks or make snide remarks. In terms of actions, he could try to sabotage Percy's relationships. For example, he might try to turn Annabeth against Percy by highlighting Percy's flaws. He could also attempt to steal Percy's thunder during important events. By doing this, he hopes to make himself look better and Percy look worse, all because of his deep - seated jealousy.
Jason might show his jealousy by being overly critical of Percy. He could nitpick at Percy's actions or decisions during quests. For example, if Percy takes a risk during a battle, Jason might comment on how irresponsible it was, while secretly he's just jealous of Percy's courage to take risks.