Firstly, is repentance to Allah sufficient for harassment, or is it necessary to seek forgiveness from the sister, with the fear of reminding her of something she might have forgotten? Secondly, is it obligatory to make up the days during which harassment and masturbation occurred in Ramadan, and how is that done? Finally, what advice can be offered in this situation?

Repentance from a sin involves abandoning it, feeling remorse, and resolving not to return to it. You must conceal your sin and not tell anyone. You must stop masturbating, as it is forbidden and has negative consequences. The cure for lust is marriage or fasting, along with guarding one's hearing and sight. As for the prayers you missed in the past after reaching puberty, you must make them up by estimating their number. Scholars differed regarding making up the Ramadan days during which one masturbated out of ignorance, with the preponderant opinion being that making them up is not obligatory. We recommend strengthening your connection with Allah by observing prayers regularly, attending religious gatherings, and keeping company with righteous individuals.