How can one get rid of the feelings of frustration and pangs of conscience resulting from ceasing to memorize by heart and from reciting silently from the Mushaf during the Quranic circle, and how can one revive the piety of Allah and trustworthiness in the heart?

The way to revive the fear of Allah (taqwa) and trustworthiness in your heart is by contemplating Allah's constant observation of you and His watchfulness, and by reflecting on the terrors of the Day of Judgment. If memorization is difficult for you, reduce the amount to be memorized and increase its repetition. Seek assistance from Allah Almighty and supplicate to Him. Do not abandon memorization entirely; rather, undertake only what you can bear of the work. Be frank with your teacher about the difficulty of the quantity, or switch to another teacher.