How does a committed young man get rid of his addiction to pornography and masturbation, and of his longing for a previous relationship before commitment?

You must take the initiative to sincerely repent from watching forbidden things and from masturbation. Allah loves those who repent and rejoices in their repentance. Know that sins are destructive, they leave an imprint on the heart and distance it from Allah. As Ibn Al-Qayyim explained, the harm of sins to the heart is like the harm of poisons to the body. They are the cause of all evil and disease in this world and the Hereafter. Among their consequences are lack of success, corruption of opinion and heart, deprivation of knowledge, and tightness of the chest.

Beware of giving in to the whispers of Satan and returning to forbidden relationships. Hasten to seek forgiveness and refuge in Allah when these thoughts arise. For if the heart is filled with love for Allah, glorification of Him, and sincerity towards Him, it will not be attached to anything else. This is why Ibn Al-Qayyim says: "If the heart is sincere and its actions are purely for Allah, the love of images cannot take hold of it; for it only takes hold of an empty heart."