My gf of 2 years dumped me today and said she wasnt ready for a long term relationship, how do i get her back?

we dated for 2 years, and as of today she left me saying that she felt i could do better, and that she wasn't really ready for a long term relationship, she just wanted to be a kid and have fun, we're both 18 and im at a loss, she was the only person i actually cared about since im usually alone and away form people, we've made it through many arguments and this came as a complete shock since wed just had an exquisite dinner together last night, can somebody please tell me how i might win her back, i truly love her, shes the only oen ive ever loved, i hate the girls at my shcool and my family pretty much has disowned me, ive lost a lot for dating her, but i gained so much from her, i learned how to be a peroson with feeligns agian. please help me