What is the guidance for a person who was committed [to the faith], then deviated and suffered a psychological condition after he was called to jihad and exhausted himself, and now wants salvation?

A Muslim is not permitted to despair of Allah's mercy after committing sins, for the door of repentance is open. The best of sinners are those who repent, and one who repents from a sin is like one who has no sin. A Muslim must perform sincere repentance and adhere to Allah's law by fulfilling commands and avoiding prohibitions, for Allah helps whoever strives in His cause.