If my ex-husband is primary on vehicle loan with Navy Federal Bank how do I....?

In 2007 husband at the time co-signed with me on a vehicle loan and when he got out of the service he stopped paying on it, we also divorced. I was the primary driver for this vehicle. The loan went into collections and I have been paying on it for 4 years now. My Jeep will be paid off in 2 months and I have made almost all of the payments with no help from him. He is primary on the loan by the way. I live in California and he lives in Texas, once I pay the lien he will get the title! My question is can he legally take the Jeep back from me and sell it? Do I need to get a Lawyer involved? I have proof that I have made all the payments myself with my bank and an auto pay setup. Can he take me off the title? Can he report it stolen? I have so many questions if anyone can maybe help me with a few it would make my day.