you are in a difficult situation.You probably had less proof or were not living together. Uscis take joint lease and financial proofs v seriously and makes most of the decisions based on that, such as, joint CC, checking/savings, transactions etc. This is a serious matter since the i485 should have been simple and most people do get approved but regardless you can try physiologist, there are actually physiologist esp. for immigration matters and they know the format to write etc...but think twice if you are going that route...your "friend" might get in some legal trouble too...you never know what will come and haunt down later down the road.
You might get a chance after you receive NTA but if your proofs are so weak then doubt that route will help you. listen to the lawyers, goodluck...