Everything you think you need in order to feel secure in a relationship will be challenged through the course of this affair, simply by your partner being the individual that they are. Even though you might be quite attracted to their individuality in the beginning, you'll gradually start to criticize them more and more for being the way they are -- or, more precisely, for being different from how you expect them to be. This dynamic will feel uncomfortably familiar to you both, as it will echo the parent-child or mentor-student relationship you shared in a past life, when you tried to help them become a better person through criticism and control.
This, however, is the lifetime in which you should try to learn, once and for all, that those tactics don't work in helping another person become who they're destined to be. The truth is, you shouldn't be 'helping' them on that level at all; their own personality and development are up to them, not you. You're no longer in charge of their education or maturation as you were in another lifetime; now, you're equals, and you have as much to learn from them as they do from you. Thus, you should focus this time around on your own education rather than theirs. Strive to treat them with fairness and respect, rather than that chilly criticism and control. Inspect your own feelings and needs carefully in order to learn more about why you feel the urge to put them in a box rather than letting them shine out as the individual that they are. Might it be that you're actually afraid they'll outshine you?