What is the way to overcome a recurring sin and the despair that comes from its repetition, despite sincere repentance and love for Allah?

What you feel is a sign of goodness, and you must adopt the means of steadfastness, such as occupying yourself with what benefits you in religion and worldly matters, accompanying the righteous, and staying away from what incites desires. And increase your fasting, continuously contemplate the attributes of Allah Almighty, death and what comes after it, and seek refuge in Allah through supplication, asking Him for firmness. And if you sin, do not despair, but rather repent, and do not tire of repeating repentance no matter how often the sin is repeated.