Whether or not you have to return the car would depend on who owns the car - - you or your ex boyfriend. If your ex boyfriend owns it and he is seeking to have the car returned, then you should consult an attorney to assist you in arguing that you contributed to its purchase and that at a minimum, you should be entitled to the money that you contributed. If the father of the children that you mention in your question is your ex boyfriend, then you should consult a family law attorney to assist you in obtaining child support. I'm not entirely sure what else you are asking with respect to your ex boyfriend but if you are concerned about the other assets you owned jointly, then you should really consult an attorney to seek to have his name removed from these assets if possible. Best of luck.
Please be sure to mark if you find the answer "helpful" or a "best" answer. (It lets us know how we are doing.) Attorney Kremer is licensed to practice in Massachusetts. Please visit her Avvo profile for contact information. In accordance with Avvo guidelines, the following disclaimer applies to all responses given in this forum: The above is NOT legal advice, and is NOT intended to be legal advice. No Attorney-Client relationship is created through the above answer.
I agree with Attorney Kremer, the fundamental question is who's name is on the title to the car and/or any loan that was taken in connection with purchasing the car. You have a claim for any contribution you made to purchase the car if your boyfriend is in fact the titleholder.