*UPDATE*
My girlfriend made contact with me about 48 hours later. She texted me and asked me to come visit her so she can appologize and talk to me face to face. I agreed to meet with her and she explained what was going through her mind. According to what she says, about 1-4 days prior to her exploding and wanting to take a step back, she was experiening stressors in her life. She said she can feel these stressors coming on and we talked about trying to provide me with some sort of advance notice so I can back off before things get bad. I know that this isn't the last episode that we will face together, but at least the communication is getting better and hopefully next time I'll be more prepard.
Yo ho Thanalyst...
Your girlfriend sounds as if she has a fearful attachment style- she pushes the relationship, then gets scared, so she pulls back.
Being in a relationship with someone like that is very difficult. You won't know from one day to the next whether she's going to be wanting to take the next step or completely finish things. The 'cause' of this kind of attachment is usually in childhood. I'm guessing she had unreliable and/or insecure childhood attachments.
In order to have a relationship with this kind of person, you need to keep things secure & stable- see each other on a regular basis, but try & have space (no contact) from each other inbetween those times.
You're going to go through quite a lot with this girl- be aware of that. You will probably never know where you stand & when you think things are going well- it will change.
Good luck!
V