Why does the questioner feel unable to remain steadfast in repentance and return to Allah despite her repeated attempts, and despite the advice of the shaykhs which she has been unable to adhere to?

Continue to repent no matter how often the sin is repeated, and do not despair of Allah's mercy. He accepts the repentance of whoever repents to Him, as stated in the Hadith (definition) Qudsi: "A servant committed a sin and said: 'O Allah, forgive me my sin...' Do as you wish, for I have forgiven you." Strive to achieve steadfastness by associating with righteous women, increasing your supplications and acts of obedience, reflecting on death, the Day of Resurrection, Paradise, and Hellfire, and remembering that Allah is watching you. This will deter you from sins and motivate you to sincere repentance.