How can one restore the fear of God, feel true happiness, despise what is forbidden and love what is permissible, and regain affection for one's wife, after falling into a forbidden relationship that led to deviation and debt?

To rid oneself of the malady of passionate love, one must sever all ties with the woman and completely distance oneself from her. What helps in this regard is to remember that leaving her is for the love of Allah the Almighty, and to fill your heart with faith, the love of Allah, and His Oneness (Tawhid (definition)), to reflect on His signs, to fear His punishment, and to supplicate to Him to turn her love away from you. The cure for this ailment is sincere devotion to Allah, for if the heart dedicates its actions purely to Allah, the love of forms cannot take hold of it, because it only enters an empty heart.