The devil’s envy is satisfied when he gets us to destroy each other.
Envy is a species of hatred, wherein the demons resent the divine graces and favor given to us and the possibility of glory for us if we defeat these evil angels. Not only that, but they’d take away even our natural happiness by causing us to sin and so to corrupt our nature, thus earning us hellfire.
They will not rest until we are pure evil.
And the devil’s pride is tickled when we worship him instead of God.
Recall that the source of the conflict is that certain angels refused the grace of charity for humans and the state of servitude that came with it.
Instead of charity, they now feel hatred for us; and instead of serving us, would rather see us bow down to them.
The remedy is for us (1) to see God for who He is: existing necessarily and being lovable essentially; (2) obey the moral law; and (3) welcome and nurture the divine grace in us through holy deeds.