What is the way back to Allah and to repent from falling into a forbidden relationship with a married man, especially with the recurrence of this sin despite the remorse?

The Shari'ah has forbidden private seclusion with a non-mahram woman and her traveling without a mahram, based on the Prophet's (peace be upon him) saying: "No man should be alone with a woman, and no woman should travel except with a mahram." Therefore, it is obligatory to fear Allah, stay away from this man, and offer sincere repentance, for Allah accepts the repentance of His servants and forgives sins.