What should be done to escape the delusion of sins and doubt in faith, especially after returning to them and losing reverence and tenderness of heart?

As for intrusive thoughts (waswas), you must strive against them and disregard them. Whenever Satan casts something of them into your heart, do not pay attention to it. Say: "I believe in Allah," then stop. And seek refuge with Allah from the cursed Satan. As for sins, the door of repentance is open, and you must sincerely strive against yourself to desist from these evils. What will help you with this is to be mindful of Allah's greatness and His constant awareness of you, to reflect on death and what comes after it, to keep company with righteous people, to avoid places that encourage sin, and to frequently remember Allah and supplicate to Him.