What should I do to avoid masturbating and reading erotic stories, and how can I be a good, faithful Muslim woman despite my repeated attempts to repent and return to sin?

Masturbation is forbidden and has great harms. One must hasten to repent to Allah and seek His forgiveness, seek Allah's help and strive in supplicating Him, stay away from stimulants, occupy one's time with beneficial activities such as remembrance of Allah, memorizing the Quran, and seeking sacred knowledge, be keen on the companionship of righteous women, and strive diligently to guard one's thoughts.