So I've(18) been dating my girlfriend(20) for almost a year now and we've had our ups and downs, but it's been an amazing relationship, but today was one of the most anxious days I've had in our entire relationship. I have a textbook case of relationship anxiety, when I don't have clarity on how she feels, I spiral and freak out. Right now I'm trying to sleep and I can't because I'm having an attack. 
Suddenly, just this morning, I wake up and she's saying how she'd be more attracted to me if I had a different body, that she feels trapped in our relationship, and that she craves meaningless sex with other people. And so naturally, I felt really hurt by that. Then we walked to university together talking about this, and she says that she misses being single. We get to school and she says she doesn't wanna talk to me, and she wants a week to decide how she feels.
About a half hour later I see her in one of the common areas, so I go over to say hi, as something financial came up that I needed to talk to her about. We make up for a while, then we go to our classes, in which, I feel fine.
Then after our classes we meet in the cafeteria. In the cafeteria I sit next to her and we talk for a little while, and she's super hostile. After I ask a few questions about how she feels, she gets annoyed with me and tells me to leave. So I do. We then make plans to see each other after school. I'm texting her periodically expressing how I feel, and she doesn't respond until night time, and she texts me that she doesn't want to see me tonight and that she doesn't wanna talk, these texts are super brief, with little to no elaboration. 
So now I'm laying in bed trying to sleep, and I can't because my mind is racing about how she might feel about me. I'm utterly terrified that she's cheating on me right now, I hope that fear is irrational. We've been through these kinds of things before, but previously they were initiated because of an argument, this time it feels so sudden. I'm hurting so much, it's like there's a burning in my heart constantly that I can't describe. What makes all of this so hard for me is how sudden it feels it happened, like we've been doing so well as a couple, then this happens seemingly out of the blue. I feel simultaneously hurt and angry that she won't talk to me, and try to resolve this together, I know we can. I just want our relationship to be perfect, because we love eachother, to the moon and back. I'm just in so much pain that she doesn't feel the way I do about her. 
I'm sorry if this isn't written well, I'm just trying to get my thoughts and feelings across.