Naruto could be one of his allies. Naruto has this knack for seeing the good in people and would probably be willing to give Obito a chance to redeem himself. Also, Sakura, with her skills as a medic - ninja, could be an ally. She might help heal Obito if he was injured during the war and see the potential in him to be a force for good.
The fanfiction could explore how Obito's identity revelation affects his relationship with the Akatsuki. Some members may feel used or deceived, while others might see it as an opportunity. It could also show how Obito's true self starts to form new bonds or break old ones within the organization, depending on how his true intentions are perceived.
One possible motive could be to use Sakura as a bargaining chip. If he has some sort of plan against Naruto or the Hidden Leaf Village, Sakura, being a close comrade of Naruto, could be very useful. He might think that by restraining her, he can force Naruto to come to a certain location or make concessions.
One sign is secrecy. If she starts being very secretive about her phone or where she's been, like always taking her phone to the bathroom or not sharing her location. For example, in a story I heard, the cheating girlfriend would never let her partner see who she was texting.
One story I heard was that a guy noticed his girlfriend was always on her phone late at night. When he finally got a chance to look, he found flirty messages with another guy. She had been making plans to meet up with this other person behind his back.
One sign could be that she becomes overly secretive about her phone. For example, she always takes it with her everywhere, even to the bathroom, and gets very defensive if you ask to see it.
One popular sakura and obito fanfiction is 'The Unseen Bond'. It delves into a world where Sakura discovers Obito's hidden past and tries to help him find redemption. Another great one could be 'Sakura's Encounter with Obito', which focuses on their chance meetings and how it gradually changes their relationship. And there's also 'A New Path for Sakura and Obito' that shows them working together to face challenges in the ninja world.