Why do people strive for power over other people?
Usually because they can't cope properly with everyday relationships, and they control because they fear being controlled. Having said that, though, it's irrational and extremely destructive. If your partner's urge to control you is causing distress, make it clear that you won't continue to live with him (or her) on that basis. Healthy interpersonal relationships are based on mutual respect, not on power and control. There's no worthwhile future in a relationship based on power. In other words, insist that he (or she) gets the appropriate therapy if they want to continue living with you.