So I'm 18 and I've been on and off with this girl who is also 18 since we were 12-13 but over the past year I've been trying to move on after she told me she had lost interest in us being together, we remained friends since we last broke up (a year ago) and talk quite often.
Obviously if she has no feelings for me I'm more than happy to remain just friends , but every time she is drunk she always rings me up to talk and always arranges to meet up and she tells me she would like to give it another try, I know she is drunk but I feel so strongly for her obviously I am going to get that little spark of hope that it could all work out, like in the films.
The day after the phonecall she stood me up for family reasons, which I am not going to say on here but they are pretty serious at the moment.

Since the phonecall which was about 2 months ago we have been talking like normal but last night I was passing by her house with a friend and I sent her a text to see what she was up to, luckily for me she was just about to arrive at her street on the bus so we finally met up. We stayed out and talked for a few hours, including my friend who is also a good friend of hers, we spoke about old times and good memories we had together back when we were in a relationship and she seemed pretty keen and gave me another spark of hope and we arranged to do something today.
So she rang me about 2 hours ago and we arranged to meet in about 2 hours from now, I text her to see what time she would roughly arrive and I told her that we wouldn't be able to come into my house, she then replied saying that she isn't going to meet me as early so that she will see me later tonight.

I text her asking if she wanted to stay at mine and what time we were going to meet up and she replied saying she can meet me at 4 but only till 6 because she is staying at another boys house -.-
So not only has she ditched our plans and has only made time for 2 hours, she is now sleeping at some random blokes house...
I have no idea what to think, I forgot to mention that when we were younger I used to play her alot and treated her really bad, I mean I used to make her walk home alone and I used to stand her up alot, I am disgusted with what I used to do and I have accepted the fact that I can't expect her to come running back now.
She has gotten her own back on me now as she has been messing me around for nearly 2 years , I totally understand if she's getting her own back but I can't help but hope there is light at the end of the tunnel...
One minute she isn't interested and the next minute she's telling me she can't stop running back to me etc etc...
I'm sorry for the long post but I wanted to make it relatively detailed so I could get the best advice possible, I'm just worried that if she gets away I may not get another chance and may regret it for a while, It's hard to let go of something that's been a part of my life for almost half of my life.

Shall I keep chasing and keep getting hurt with a chance of it all working out? or shall I try to move on and hurt and risk losing somebody that has been a part of my life for so long in reletivity to how old I am?
I would be greatful for any advice, thanks.