How can a person commit a sin despite their intense love for God and the strength of their faith in Him, and why do they repeatedly return to it despite their repeated attempts to abandon it and their struggle against themselves?

Falling into sins is a sign of weak faith. Therefore, the questioner should strengthen her faith, and this is achieved by observing the obligatory duties, reciting the Qur'an with reflection, increasing the remembrance of Allah, choosing righteous companions, attending gatherings of knowledge, and making supplication.