What is the advice for a young man who is experiencing wavering in his steadfastness and his relationship with God, as he feels weakness of faith and worries after a period of repentance and spiritual uplift?

Worries and sorrows come from Satan to grieve you and to stand between you and uprightness. Be patient, persevere, and sincerely repent. Turn to Allah, supplicating humbly that He grants you true uprightness. Accompany the righteous and good people, and strive to increase in supererogatory acts of worship after the obligatory ones. Turn to Allah with sincerity, have a good opinion of Him, and do not surrender to Satan. Rather, counter him with more obedience and turning to Allah.