my story with ex

Let explain my story with my ex girlfriend. We have had a very long relationship with her for 3 years but we parted ways. We see each other from time after time and i try to make things together again. But she is especially character. We only see each other at night and stay in her car as always. If not, we sit in my home and just talking about us. I talked to her for a long time to be a again together and get things to the right way, move on forword for us, but she only wants to see me when she can. Even all the time, she doesn't want to introduce me with their parents, which amazes me a lot. I don't know what to do, to leave it her and look for a new girl or try to make things right.