I hear how much you love her, and it's completely understandable that you're feeling hurt and confused right now. But as someone looking from the outside in, I have to be honest with you: this situation is heavily one sided.
At 37, after two years of dating, she absolutely knows whether or not she wants to marry you. The biggest red flag here isn't just that she said no it's that she rejected your proposals twice but still feels perfectly comfortable asking you to fund her life, pay her bills, and use your car. A partner who truly respects you and your feelings would step back from taking your money after turning down a marriage proposal.
You are ready to build a life, and she is treating you like a financial safety net. My advice: cut off the financial support immediately. Tell her you need to focus your resources on your own future right now. Her reaction to the money stopping will tell you everything you need to know about how she really feels about you. Don't waste your best years on someone who only wants your wallet.