How can the questioner rid himself of his bad psychological state and regret over what has passed of his life, return to his studies, and repent after his addiction to illicit relationships, and how can he rid himself of his attachment to a disabled girl, and how can he compensate for what he has missed?

Realizing a mistake is the beginning of rectitude. The self-reproaching soul that blames its owner for sin is the soul of a believer. Therefore, praise Allah for this soul and hasten to sincere repentance, even if the sin is repeated. Cut off your relationship with the girl immediately and be firm in your resolve. Do not despair of striving for marriage, and ask Allah for help. If you do not find it, then be patient and fear Allah, and follow the means that assist in good and prevent evil.