Often, his jealousy is manifested in his actions towards James. He might try to outdo James in academic or magical feats, all because he wants to prove that he is better than James, especially in Lily's eyes. And when it comes to Lily, he may be secretly longing for her attention while trying to hide his feelings because he knows she is with James.
Snape's view of James might not change much at first. He has such deep - seated hatred for James due to their past. But if the fanfiction shows James in a more positive or sympathetic light, he may start to question his long - held beliefs about him, just a little bit.
Snape might be portrayed as a more vulnerable character in this fanfiction. Away from the pressures of the wizarding world, he can show his true emotions to Lily.
Often, James is shown as either the bully he was in the books or as a more nuanced character who has grown past his school - day flaws. Fanfiction can give him a chance to redeem himself in Snape's eyes. Snape, on the other hand, is usually portrayed as the long - suffering victim of James' bullying, but also as a complex character with his own motives and secrets.
It would strain their relationship even more. Snape's love for Lily was already on shaky ground due to their different paths. Seeing her with James would make him feel like she has completely chosen the other side, and he might start to resent her a bit.
In fanfiction, James Potter is sometimes portrayed as a more complex character than in the original books. He might be shown as having deeper regrets about his bullying of Snape. On the other hand, Severus Snape can be presented as even more of a tragic figure, with his love for Lily being explored in more detail. His bitterness towards James can also be magnified.
Guilt and redemption can be a theme too. Snape's actions were often driven by his love for Lily and his guilt over her death. Fanfictions may expand on this, showing how he tries to make up for it in different ways. Also, the theme of loyalty - Snape's loyalty to Lily even after her death is a powerful concept that fanfictions often explore, sometimes by creating scenarios where Lily somehow comes back or is still present in a way that tests Snape's loyalty.
Love and jealousy are very common themes. Snape's unrequited love for Lily while she is with James creates a lot of jealousy. It often drives the plot as Snape's actions are influenced by his feelings.
In many fanfictions, Snape's jealousy of James and Lily can be deeply rooted in his unrequited love for Lily. Snape had a complex relationship with Lily from their childhood. He loved her deeply, but she fell in love with James. This led to his intense jealousy. His envy towards James was not just about Lily's love, but also about James' popularity and charm which Snape felt he lacked.
Unrequited love is a very common theme. Snape's love for Lily that was never fully reciprocated is often explored in depth. It adds a lot of emotional depth to the stories.
If Snape walks in on Lily and James in fanfiction, his character could develop in a more bitter and vengeful way. The sight of Lily with James would be like a dagger to his heart, and he might be driven further towards the dark side. He could start to plot more maliciously against James, using his skills in potions and dark magic to his advantage.