What is the way to remain steadfast in repentance, abandon bad habits, stay away from temptations, and regain the sweetness of faith, given the frequency of relapses and the feeling of hypocrisy?

What you mentioned is not pure evil; rather, it contains good that invites optimism and hope, for Allah Almighty says: "And [there are] others who have acknowledged their sins. They had mixed a righteous deed with another that was bad. Perhaps Allah will turn to them in forgiveness. Indeed, Allah is Forgiving and Merciful." [At-Tawbah: 102], and the Messenger of Allah, peace and blessings be upon him, said: "Whoever performs a good deed and is pleased with it, and performs a bad deed and is grieved by it, he is a believer." And a believer fluctuates between an accepted good deed and sins forgiven through his repentance, seeking forgiveness, and erasing bad deeds with good ones.