My sister and I were born a year and a half apart. She has treated me horribly since we were kids-stealing my things and talking behind my back. She once confessed that she’s jealous of me because our mother often compared us. I’ve tried to improve our relationship and even helped her land a job at my company when she was unemployed.

But she has repeatedly violated the one request I made when we started working together: not to discuss my personal matters with the staff. I’m so hurt I’ve considered looking for a new job or moving to another city. When I confronted her, she acted as if it were no big deal. What should I do?

Sibling rivalry is common and can play out in childhood, adolescence and, yes, even adulthood. But this situation has gotten out of hand, and you won’t fix it by continuing to placate your sister. When you do that, it sounds as though her behavior gets worse.

I get the impression that you two are playing out “good girl” and “bad girl” roles that were assigned to you. When parents lock children into this rivalry, as your mother may have done with her comparisons, it can lead to a lifetime of polarization.

No amount of rule setting for your sister will stop her from acting out. Confronting her again won’t work either-she’s completely insensitive to your needs. You both should get professional help. Find a psychologist or therapist to help you wade through the animosity. You can begin your own healing by refusing to be your sister’s victim. She needs an audience to act out; don’t give her one. Stop internalizing her words and letting her drag you up and down an emotional roller coaster.

And certainly don’t run away. Taking another job or moving to another city just sends the message that your sister is in control. A good way to handle her blabbing about your personal business is to keep a positive attitude and conduct yourself in a professional manner. Trying to set the story straight or exposing your sister’s motives will only create more drama-and people will think you’re both emotionally unstable. But being your best self with your coworkers will show them that you’re not the woman your sister makes you out to be.