What is the ruling on one who promised not to return to a sin, then broke his promise, and how can he be saved from Hellfire, enter Paradise, and attain Allah's pleasure?

Fulfilling a promise is a characteristic of believers, while breaking it is a characteristic of hypocrites. It is obligatory for whoever makes a promise to fulfill it, especially if the promise is to Allah, the Almighty. It is necessary to hasten to sincere repentance to Allah and to resolve not to return to sin.