How can one repent from masturbation and emerge from a state of depression, while desiring to serve Islam and the Arab world and achieve academic success, especially given the limited time before exams?

Your hatred for Allah and your feeling that His actions contain injustice is one of the greatest sins and the ugliest forms of disbelief. It is a denial of His words, the Most High: ﴿Indeed, Allah does not wrong even an atom's weight﴾, and His words, the Most High: ﴿Indeed, Allah does not wrong people at all, but it is people who wrong themselves﴾, and His words, the Most High: ﴿And your Lord is not ever unjust to His servants﴾. The psychological crises, anxiety, and thoughts of suicide you are experiencing are only due to your disobedience to Allah, the Most High, for Allah says: ﴿But whoever turns away from My remembrance – indeed, for him is a constricted life﴾. Hasten to repentance and do not despair of Allah's mercy, for Allah loves those who repent, ﴿Indeed, Allah loves those who repent﴾. Be diligent in performing prayers, remembering Allah, abandoning masturbation, and doing good deeds, and you will notice that you have become a different person.