I can relate to your frustration and annoyance. We all go through this. Don't give up.
If she told you she's not interested in that firm way, the general rule is to move on. Why would you waste time trying to persuade a girl, who doesn't want to date you, to date you? You could better spend that time investing in yourself and meeting other women who actually want to date you.
I will say it seems like you didn't invest in the relationship enough. Women generally want a man to lead the relationship. You say that you texted and chatted to her for your months but sometimes met her. If you like a girl, you should try to meet her a bit more than sometimes. I'm guessing that this girl didn't see you as taking an active role in the relationship. She may even think that since you guys so rarely met, you might not be that interested. It could also be the case that she just was messing with your emotions. I don't know. Only you can really figure it out, but I would guess that one thing you could have done differenty was to ask her out on a date.
I know that this girl is stick in your head. Your best bet to get around that, is to go out and meet other women. There are a zillion of girls that are as attractive and amazing as this girl was. Walk down the street and you will see cute girl after cute girl after cute girl walk by you.
Invest in yourself. Figure out what you want to do. Improve your social life. Join a meetup.com. I personally found that having a progress journal helped. I spent a whole summer (plus some) hitting on 2+ girls a day. I actually got my first date in years just by telling a girl that I thought her dress looked amazing. I still fumbled a lot. I still was nervous. I still lacked self-esteem. But I tried.
Good luck and stay in touch!