Well, it's simple. In the fanfiction world, Ron is sometimes portrayed as jealous because Harry is the famous 'Chosen One' and Hermione is super - intelligent. When they spend time together, Ron may think they are forming a clique without him. He's also a bit insecure, and seeing Harry and Hermione's camaraderie might make him fear that he's not as integral to their group as he wants to be. So, that jealousy pops up.
Well, in addition to Bella and Emmett, there could be other characters from the original source material (assuming it's based on something like Twilight series). For example, Bella's friends might play a role, like they could be there for support or they might be shocked and have to deal with their own feelings about the situation. Emmett's family or vampire clan (if relevant) could also be important characters, as they might have their own reactions to the pregnancy.
Well, in some fanfictions, Raven's jealousy could be triggered by someone flirting with the person she has feelings for. For instance, if it's a story set in a high school AU, and there's a popular student who starts flirting with her crush. Raven would then show signs of jealousy like glaring at the person, or trying to get in between their conversations. There could also be a situation where Raven is jealous of another character's powers. Maybe in a superhero - themed fanfic, another hero has a really flashy power and is getting all the media attention, making Raven jealous as she feels her own powers are being overlooked.
One common theme is Hinata's unrequited love. Since she has strong feelings for Naruto but often doubts if he feels the same, seeing him with others can easily make her jealous. For example, in many fics, she might see Naruto being close to Sakura and her jealousy stems from her fear of losing him to Sakura.
A common scenario is when Naruto is given a special mission or task that Sasuke feels he should have been chosen for. Sasuke's pride and his competitive nature with Naruto make him jealous. He might think that Naruto is being favored over him.
In many Sasuke - gets - jealous - of - Naruto fanfictions, it often stems from Sasuke's insecurities. He may be jealous of Naruto's natural ability to make friends easily. Naruto has a charisma that draws people in, and Sasuke, who has always been more of an loner, may feel left out or envious. For instance, if Naruto is praised for his skills in a particular area, Sasuke might feel jealous as he also wants that kind of recognition but is too proud to show it in a normal way.
In fanfiction, the jealousy of Jessie towards James might be a creative way to explore their characters more deeply. It could be that the author wants to show Jessie's insecurities. For example, if the fanfiction has James being praised for his skills or looks, Jessie, who is often portrayed as competitive, might feel jealous because she wants that kind of recognition too. Also, it could be related to her possessive nature over James as a partner in their Team Rocket adventures.
In many Naruto fanfictions, Sakura can often be depicted as getting jealous quite a bit. She has strong feelings for Sasuke, and when she sees other girls getting close to him, it can trigger her jealousy. For example, in some fanfictions where a new girl character is introduced and shows interest in Sasuke, Sakura's jealous side comes out strongly.
Well, one possible plot development could be that they face a lot of challenges from their families and friends. Since it's an unexpected situation, there might be initial shock and disbelief. Maybe they have to deal with the judgment of the community they are in. They would need to figure out how to prepare for the baby, like finding a proper place to live and getting necessary supplies.
In many fanfictions, Natsu might get jealous of Lucy when she spends time with other characters. For example, if Lucy is training with Gray more often, Natsu could feel left out and jealous. His jealousy might stem from his deep bond with Lucy, which he may not fully understand himself.