Even though Mon - El leaves, their relationship can still develop. Kara could keep a journal for the baby, writing about her feelings for Mon - El. When Mon - El returns (if he does), he could read it and realize how much Kara truly loved him. Also, Kara might have dreams or visions of Mon - El during her pregnancy, which could show that their connection is still strong on an emotional level.
She might initially be heartbroken. Kara, being strong - willed, could focus on taking care of herself and the unborn child. She may turn to her friends at the DEO for support, like Alex, who would be there to help her through the difficult time both emotionally and physically.
Their relationship would likely become more protective. Mon - El would be constantly worried about Kara's well - being and that of the baby. He would be more vigilant and might even become overprotective at times. Kara, on the other hand, might struggle with accepting too much help as she is used to being the one who protects others. But she would also have to learn to rely on Mon - El more, which could strengthen their bond in a new way.
He might leave to protect Kara and the unborn child. Maybe he discovers that there is some kind of danger following him that could put them in jeopardy, so he decides to sacrifice his time with them to keep them safe.
One popular Kara and Mon - El pregnant fanfiction might be 'A New Beginning'. It focuses on how they navigate their relationship while expecting a child. It shows Kara's struggle between her superhero duties and impending motherhood in a really interesting way.
You can try Archive of Our Own (AO3). It has a vast collection of fanfictions, and there are likely to be many about Kara and Mon - El being pregnant. Just use the search function and type in the relevant keywords.
In this fanfiction scenario, Kara being pregnant and Mon - El leaving could lead to a complex story. Maybe Mon - El leaves because he fears for Kara's safety due to her pregnancy and his past or some external threats. Kara is left heartbroken and pregnant. She may initially be in denial about Mon - El's departure, but then has to face reality. As she goes through the pregnancy, she could meet new people who help her, like other superheroes or just kind - hearted civilians. And throughout the story, there could be a lingering hope that Mon - El will return, but also a growing sense of self - reliance in Kara as she prepares to be a mother alone.
One possible plot twist could be that Kara's pregnancy somehow affects her superpowers. Maybe she loses them temporarily, which adds a whole new layer of vulnerability and drama. For example, she has to rely on her friends and Mon - El more than ever to protect her and the unborn child. Another twist could be that there are some unexpected genetic mutations in the baby due to their unique alien heritages, leading to a race against time to find a way to ensure the baby's health.
I'm not entirely sure specifically as it could vary greatly. But generally, a 'fanfiction' about Supergirl and Mon - El might explore a relationship that has elements of abuse in the context of the story created by the fan writer. It could be about power imbalances, emotional abuse, or other complex relationship dynamics within the framework of their characters as known from the Supergirl series.
Love is a very common theme. Since their relationship is a central part of the stories, it often explores different aspects of love like first love, unrequited love, or love that overcomes obstacles.