Well, Harry might be jealous because Bill and Fleur seem to have a very stable and loving relationship. Harry, on the other hand, has lost so many people he cares about. He may long for that kind of connection and seeing Bill and Fleur together makes him aware of what he lacks. Additionally, Fleur is a very confident and charming person, and Harry may envy Bill for having such a partner.
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.
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.
His jealousy might make him a bit withdrawn from Bill.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.
One possible reason could be that Dean is better at something that Harry secretly wishes he was good at. For example, if Dean is really popular among their peers and Harry feels overshadowed. Another reason might be related to a girl they both like. Maybe the girl shows more interest in Dean, and Harry can't help but feel jealous.
In some fanfictions, Fleur might leave Bill for Harry because she realizes that Harry has a certain selfless quality that she admires more. Harry's constant fight against evil and his willingness to sacrifice himself could be very appealing to Fleur. Also, it could be that the fanfiction is set in a situation where Bill is involved in something that Fleur morally opposes, and Harry represents a more morally upright choice for her.
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 common reason could be Naruto's growing popularity and strength. As Naruto becomes more powerful and well - liked in the fanfiction, Sakura might feel overshadowed. Maybe she's jealous of the attention he gets from their peers or even from her own friends.
Maybe it's because of Naruto. If Hinata has a closer relationship with Naruto than Sakura does in the fanfiction, Sakura could be jealous. After all, Sakura has her own feelings for Naruto.
One reason could be Jason's popularity. Maybe Jason is getting more attention from their peers or the gods, which makes Percy jealous. Another might be related to a girl they both like. If the girl shows more interest in Jason, Percy could feel jealous.
It could be that Bella has a love interest that Lauren also fancies. In fanfiction, love triangles are common. If the object of affection shows more interest in Bella, it would make Lauren jealous. For example, if there's a guy both of them like, and he always chooses Bella over Lauren.
There are several possible reasons. Firstly, if Michael has a higher social status or is more popular among their peers, Harry might feel jealous. In a school - based fanfiction, for instance, Michael could be the star of the school while Harry is more of an outcast. Secondly, if there is a special opportunity, like a quest or a role in a play, and Michael gets it instead of Harry, that could trigger jealousy. Also, if Michael has a better relationship with a mentor figure, say a wise old wizard in a fantasy setting, Harry may feel left out and jealous as he desires that guidance and connection too.