In a fanfic, Sasuke's jealousy could be a catalyst for change in their relationship. Let's say Sasuke has always been aloof towards Sakura. But when he starts to feel jealous, he becomes more possessive. This could either drive Sakura away or draw her closer. If she is drawn closer, she might start to understand Sasuke better and they could start to build a deeper connection. They could go on missions together where Sasuke's jealousy comes to the surface in different situations, like when another ninja flirts with Sakura.
The relationship could start with Sasuke being secretly jealous of Sakura's closeness to someone else. He might not show it at first, but little actions would give it away. For instance, he might glare at the other person when they are around Sakura. Sakura, being perceptive, could start to suspect something. This would create an interesting dynamic as she tries to figure out what's wrong with Sasuke.
To develop their relationship in a fanfic, we could have Sasuke's jealousy stem from his own insecurities. Maybe he feels that he doesn't deserve Sakura because of his past actions. So, when he sees Sakura being happy with others, he gets jealous. Sakura, who has always loved Sasuke, tries to reassure him. This could lead to some really heart - to - heart conversations between them. They could also have shared experiences where they overcome their problems together, with Sasuke gradually learning to trust in Sakura's love and letting go of his jealousy.