No, the car would never "be yours" unless you took legal action against him.  What happened here was what is considered under the law a "bailment" meaning that he entrusted the car to you and then you "converted" the property by selling it and making it your own.  This is the civil end of the matter.  The criminal end of the matter is that you "stole" the vehicle, but I bet that when you speak with a criminal attorney the facts will not sustain the elements of the crime for which they are attempting to charge you.  Get legal help here asap.  You need to know both ends of the matter - civil and criminal - and have a plan for dealing with both.