Can I be sued for not paying off a car I signed a bill of sale for?

I bought a car from a guy in December. I paid $300 down and signed a bill of sale which states I would pay $100 a week until the remainder was paid off. The car was $1800 in total and I now owe $1500. My husband ended up having surgery and is off work. I had a miscarriage and am off work. Things have been hard and I'm faced with paying my immediate bills or paying for the car. The seller and I have stayed in touch and I at no point have dodged him and am not intentionally refusing to pay. I just can't pay right now. I don't feel comfortable giving the car back due to the fact that I've put a lot of money into it to get it running. The car was supposed to have a brake line issue and that's it. It ended up with much more and I've spent well over $1000 to fix everything. He signed the title over to me upon purchase and the car legally belongs to me. He's not a lienholder. I've tried talking to him and he is not having it. He won't wait any longer. I've tried explaining my situation and he wants money now. I'm nervous because this car is my only form of transportation. I haven't made any payments. I'm not trying to lie my way out of anything. I've been upfront from the start. I have no criminal record and don't want to start now. He has told me that the judge can issue a warrant for my arrest and make me sit in jail.