Advice for One Who Has Been Afflicted by Sins and Then Repented

Q: I am a high school student. I used to be committed, loved the Noble Qur'an, and was passionate about knowledge. Then my situation changed, as a group of bad people gathered around me. I began to engage in the secret habit and committed many grave sins, such as sodomy, messing with people's daughters, and looking at the private parts of neighbors. Outwardly, I would talk to my classmates about religion and the affairs of Islamic groups in the school, the mosque, and the home.
I have tried repeatedly to quit these sins but could not. I want a healing cure commanded by Allah and His Messenger. I will not find peace until I hear and read from your eminence. May Allah keep you for Islam and grant you patience and well-being. Peace be upon you, and Allah's mercy and blessings. A servant among Allah's servants.

A: And upon you be peace, and the mercy of Allah and His blessings. After that:
I ask Allah by His most beautiful names and His exalted attributes to grant you sincere repentance, to expand your chest for the truth, to guide you to the company of the righteous, and to protect you from the company of the wicked. He is the best of those asked. I advise you to make sincere repentance, which includes three things:
1 - Regret for the past regarding all sins.
2 - Quitting them all out of fear of Allah and reverence for Him.
3 - A sincere resolve not to return to them, out of sincerity for Allah and desire for what is with Him.
When you have done this, be glad of forgiveness and a good outcome. May Allah guide us and you to what pleases Him, and protect us and you from the whispers of Satan and from the evil of the self and bad deeds. He is the All-Hearing, the Near. Peace be upon you, and Allah's mercy and blessings.