Will Allah forgive a girl who regrets having exposed herself to a young man via camera, and the young man's threat to publish the video? And what is the way to get out of this difficult situation?

One must hasten to sincere repentance, fulfilling all its conditions, while maintaining a good opinion of Allah and not despairing of His mercy. There is no harm if the motivation for repentance is the fear of exposure, alongside the fear of Allah. It is advisable to frequently supplicate for well-being and concealment (of sins), and to recite the reported supplication when fearing enemies. The man should be advised kindly and the virtue of concealment should be explained to him. If he does not respond, he can be threatened with resorting to legal action. It is permissible to deny the act, use dissimulation (tawriyah), or outright lie to avert harm. One is strongly warned against contemplating suicide, as it is a grievous disease that leads to eternal misery.