If the title is in his name, then he, not you, is the owner of the car--it's his vehicle. He may have let you use it, but he never transferred ownership to your name. Even if he promised to do so, that would be a gratuitous promise (one unsupported by consideration, or by an exchange of something of value), and a gratuitous promise is not enforceable. In short, no matter what he may have said to you, he never actually gave you the car, and you do not appear to have a legally enforceable right to make him do so.Since it is his car, if you do not give it back, you would be stealing; so yes, he could report it to the police.