What should I do about this girl?

(sorry if this long)ok first here some of the history behide me and her.I known her for a over a year now. We dated like 5 times.now I just feel like I shoulda left her alone a long time ago. We just friends right now. I wasted so much time. Trying to be with her ect. Ect.. I mean seriously months of my life I probably wasted on her. If I woulda left her alone. Something great might had happen to me. But I wont know since I wasted my time. The other day we got in a argue. Like alway we fight. She act hmm she act like a kid sometime.(she 14 im 15 btw). Like come on grow up. She alway over react about something. Like ok I cheated on her before.yea I know it was wrong. At least I can admit it.like last time we was dating.I would try to be truthful about something. And boom she was just say some stupid things, like “ oh oh ok so you dont wanna be wit me no more”. Like what seriously when did them words come out of my mouth.this is the 1 problem of all them.then like she would be mad about something or sad. Me trying to be a good friend or boyfriend.try to figure out what wrong, or how I can help,like you know she never tell me. Or nothing. So how can I help if she wont tell me.I just want to tell her to go f* off. I can be the best person to peoples.as much as I want to tell her off. I cant there a part of me. That wont let me say it. Im close to the point where I just wont care no more.when I first met her. She was perfect. Everything I wanted. She had inside. I dont see where it fell apart off. But still I dont know if it time. To leave her alone.. Or what I just dont know what to do now. I was alway there for her. I try and try so many times. Oo I made a mistake who dont make mistakes.I dont what to do about her no more.any tips? Advice? Please thank.