What do I do since my car title has been taken away from me by my ex?

I don't know what to really do. My boyfriend or ex even, has the title to the car—which is under both of our names with a and/or— and the keys because I wrecked the front end one day. Nothing is damaged internally other than the tranny cooler and the radiator, but he took the title out of my jewelery box one day and took it with him to his mom's house. Well, I know that it's somewhere in that house along with the keys since he too stole them out of my bag as well. What makes it even better is that the car is at his mother's house too. I have a feeling that I'm unable to do anything because he has the title and the key to the car. However, I have the Bill of Sale and proof that I paid for the insurance for the car under his name more or less. And now, he's trying to sell the car for a truck for this lawn mowing business he's trying to start. Is there anyway for me to get my possessions back?