Why does one feel distress and depression instead of happiness and a sense of ease after refraining from an act they desire, despite Allah Almighty promising a good life and happiness in this world and the hereafter to those who do righteous deeds?

Allah Almighty has promised the believers who do good deeds a good life in this world and a good reward in the Hereafter. The good life includes comfort, lawful sustenance, contentment, happiness, and righteous work performed with joy.

Whoever abandons familiar habits and customs for the sake of Allah with sincerity may find it difficult at first, but this difficulty quickly turns into pleasure. Allah will compensate him with something better, and the best compensation is intimacy with Allah, His love, and tranquility of heart.

Continued patience and striving against the self and Satan lead to happiness and inner peace. The sadness that afflicts the penitent at the beginning of their path is temporary, for the penitent is rewarded for their struggle.