"No, you are my partner."
Translation:Nein, Du bist mein Partner.
It shouldn't be. In fact, once you complete the question, whether you've gotten the answer correct or not, please report the error.
It depends on case and gender of the noun. In this case, "Partner" is masculine, and the case is nominative, so it is mein.
Also, take note that "du" no longer needs to be capitalized but you may come across it spelled that way in older texts. http://german.about.com/library/weekly/aa020919b.htm