You can start by looking on fanfiction.net. It has a large collection of Pokémon - related fanfics, including many about Jessie and James. Just use the search function and type in 'Jessie x James' to find relevant stories.
They might love fanfiction because it offers new perspectives on their own lives. In fanfictions, their characters can be developed in ways that the original show might not have explored fully. For instance, they could be portrayed as more complex individuals with deeper backstories.
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 the 'jessie and james adopt ash fanfiction', perhaps they would start living in a different kind of home. Since Jessie and James are from Team Rocket, they could use their resources to give Ash a more luxurious or unique living environment. And Ash could introduce them to his Pokémon friends in a more personal way. He might also learn some of the sneaky tricks that Jessie and James know, which could be both good and bad.
Comedy - centered fanfictions could be great too. Given their somewhat bumbling and comical nature in the show, a fanfiction full of humorous situations, like them trying to cook a meal for their Pokémon but everything going hilariously wrong, would surely make them laugh and thus be something they'd enjoy.
Well, perhaps Ash is in a different dimension or a strange, uncharted area where he's in trouble. Jessie and James could be on a mission of their own in that area and stumble upon Ash. They realize that they need to save him because, despite their past differences, they know Ash is important to the Pokémon world. They might have to combine their resources, like Jessie's Wobbuffet and James's Cacnea, to fight off any threats and get Ash back to safety.
Perhaps a major plot twist would be that Ash starts to act more like Jessie and James. He might become a bit more mischievous or devious in his ways of catching Pokémon. This would be a huge change from his usual good - natured self. Also, there could be a plot twist where the three of them find out that they are related in some unexpected way, like they share a long - lost family connection. This would add a whole new layer of complexity to their relationship and the story as a whole.
Maybe a fanfiction where Jessie and James discover a rare and powerful Pokemon that has the ability to grant wishes. But they have to go through a series of challenges set by other mysterious Pokemon to earn the right to make a wish. This could lead to a lot of character development as they face their own greed and learn about true friendship along the way.
Well, next in the fanfiction, Jessie might try to outdo James in whatever is making her jealous. For example, if James is getting praised for his Pokemon - catching skills, Jessie will probably go on a crazy Pokemon - catching spree to show she's better.