How are stolen soul pieces used by the thief? How to stop it?

Stolen soul pieces can only be used while the person who stole them has a consistent source of energy from the person the soul pieces belong to. If they can’t drain your energy, they can’t activate your soul pieces, which means they can’t be used. It’s also one reason why abusers will keep their victims around them as long as possible; they need that attention and energy in order to continue using the stolen soul pieces.