Is what I mentioned—committing sins, abandoning prayer, and engaging in wrongdoing due to not being married—considered polytheism (shirk) with Allah, despite my sincere repentance and intense remorse?

No matter how great your sin, the pardon and mercy of Allah are greater. He forgives all sins for whoever repents to Him, even shirk (polytheism), as 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.'" Turn over the page of the past and approach your Lord, striving in His worship and increasing in good deeds. Know that Allah's choice for you is better than your choice for yourself, and His planning for you is better than your planning for yourself. Repent to Allah with sincere repentance from all sins, especially abandoning prayer, for it is one of the greatest destructive sins.