If the car is registered in your husband's name, it will be difficult to prevent him from physically taking it away from you without a court order. It would appear that the time has now come for you to start those divorce proceedings, and in that context, you can go into court and ask for an order that you be given the exclusive use and possession of that vehicle.
If the car was purchased during the marriage, I can assume it is community property, which means you already own half of it whether your name is on title or not (there are a lot of possible exceptions to the statement I just made, but for these purposes we can go with that). You really should discuss this matter further with an experienced family law attorney. Good luck.
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