One popular one might be 'The Labyrinth of Love' which delves deep into their relationship. It shows how Sarah overcomes her initial fears of Jareth and they start to understand each other on a deeper level.
There is a fanfiction called 'Love Beyond the Labyrinth' where Sarah, after getting lost again in the labyrinth, discovers a new side of Jareth and they start to explore their romantic feelings. It has really detailed descriptions of their emotions and the magical setting.
One great fanfiction could be 'The Enchanted Kiss' where the kiss between Jareth and Sarah is a turning point in a magical adventure they embark on together. It delves deep into their complex relationship and how the kiss changes their dynamic.
There might be a fanfiction where Sarah has to team up with Dark Jareth against a common enemy. They start to understand each other better during this adventure. For example, they face a powerful dark force that threatens both their worlds.
One great Jareth and Sarah fanfiction is 'The Labyrinth's Echo'. It beautifully explores their relationship post - the events of the Labyrinth. The author really captures the essence of Jareth's allure and Sarah's growth.
The relationship might become more intense. With the pregnancy, they have to rely on each other more. Jareth may show his softer side as he takes care of Sarah, and Sarah might start to see him in a new light, beyond the intimidating Goblin King.
There could be some out there, but a lot of fanfiction platforms have rules against explicit content. You might have better luck looking for more general Jareth and Sarah fanfiction on Archive of Our Own (AO3). It has a large collection, and you can filter by different themes and ratings to find something that suits your taste, but stay away from inappropriate stuff.
A common theme is the exploration of their unspoken connection. Since in the original there's a certain tension between them, fanfictions often expand on that, like in 'The Unspoken Bond' where it's all about their unacknowledged feelings for each other.
You can start by looking on Archive of Our Own (AO3). It has a large collection of fanfiction for various fandoms, including ones about Sarah and Jareth's love.
Perhaps a plotline where they have to deal with the differences in their worlds. Sarah comes from the human world and Jareth from the magical realm. Their married life could be about finding a balance between the two, like how they decorate their home, half with human items and half with magical ones.
One interesting plot could be that Sarah, after being kidnapped, discovers a hidden side of Jareth's kingdom that he has kept secret from everyone. She finds out that there are other captives there who are being held against their will for reasons she has to uncover. As she tries to escape and free the others, she starts to see Jareth in a different light, not just as a captor but as a complex being with his own motives and past traumas.