What would you do if you were in a casual relationship and she falls for someone else?

So, I have been in a casual relationship with this 19 year old bisexual girl for 3 months now. I am 17 and also a girl.

She was very much into me at the start due to me keeping mystery and playing a little hard to get.

Then we went to a festival for 5 days together and I guess it was pretty obvious I was into her.. She also didnt seem to have the best of times because she was sad from drug comedowns and also because she felt left out with her friends.

After this festival she was pretty distant with me and I put it down to the fact she was sad and was busy with preparing for university.

She then spent £20 to get a train to come and see me and everything was normal: we had fun, we had sex, we kissed, we cuddled.

Then she went home and still continued to not put that much effort into communicating with me.

I expressed this to her and she told me that she just wants something casual and see where things go.

Then I asked her "Are you speaking to anyone else?" and she admitted to speaking to this other girl and she really likes her and thats why shes been distant with me because shes been distracted by this other girl.

She also told me that shes just very confused because she does like me also and her feelings for me haven't changed its just her feelings for the other girl have grown. But her and that girl are just friends and its not like that and she doesn't think it will go anywhere.

The girl and her are going to the same university but the girl is going travelling for a year. 'My girl' is on holiday for two weeks right now then has a week at home before she heads off to university which is a 5 hour train ride away from me.

I was very angry and sad and told her I don't think we should talk anymore. She seemed pretty disappointed because she wanted to continue speaking to me and she does like me shes just very confused but if she was making me sad and not speaking to her would make me happy she said that I should do that.

So we said bye and I haven't texted her for two days...

But I'm starting to want to text her. I wish I could text her and she would tell me shes missed me and shes made a mistake.. but lets be honest I am living in a dream world - she was more into that other girl as she gave her more attention :/

I am not sure what to do... What would you do?