Do you have a 'frenemy'?
A frenemy refers to two opposing parties, be it in personal relationships or in large scale interaction between nations, organizations, political parties, etc., that are mutually beneficial, yet are at odds to be mutually destructive.
http://en.wikipedia.org/wiki/Frenemyhttp://www.cnn.com/2007/LIVING/personal/08/24/frenemies/index.html