Can a young man addicted to pornography and pre-marital sexual acts truly repent and abandon these practices, especially given his repeated attempts to cut off illicit relationships and return to Allah with a sound heart, and what are the ways he can follow to achieve that?

For every sin there is repentance, no matter its magnitude, even disbelief (kufr). Allah Almighty mentioned concerning disbelief: "Say to those who have disbelieved, if they cease, what has passed will be forgiven for them. But if they return, then the custom of the former peoples has already gone forth." (Quran 8:38). You can review previous fatwas for advice on repentance and avoiding a return to sin, such as Fatwa (definition) 78014 on the benefits of lowering one's gaze. We ask Allah for purification and protection.