What is the ruling on one who relapsed last Ramadan and returned to sin, missing the opportunity for repentance, and is it still possible for him to repent despite repeated sins and feelings of despair?

The door of repentance is open and will not close until the sun rises from the west. No matter how many times a sin is committed, Allah accepts sincere repentance, and the one who repents becomes as if he had never sinned. Allah Almighty says: "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" A Muslim should not tire of repeatedly repenting, no matter how many times the sin is committed, while adhering to its conditions: abandoning the sin, resolving not to return to it, and regretting having committed it.