How can one achieve sincere repentance and elevate the soul after engaging in forbidden acts and suffering from weakness of spirit and depression?

You did well by repenting from abandoning prayer and engaging in relationships with girls, as both are forbidden. Abandoning prayer is a grave sin; some scholars even considered its perpetrator to be a disbeliever. Relationships between the sexes are a gateway to evil. Do not succumb to the whispers of Satan, who portrays returning to girls as a cure, for this is an ailment, not a remedy. Renew your repentance, for tribulation descends with sin and is lifted by repentance. Your eagerness for what brings you closer to Allah and distances you from Satan will bring you tranquility and self-confidence.