I (19M) took leave to visit my girlfriend (18f) because she begged me to see her graduation. Then she broke up with me.

I'm in the military and have been dating my (I guess ex) for a year. My brother can't take leave as on a whim as I can so I was originally going home at the same time as him, also when all our friends would be home.
My girlfriend begged me to come to see her graduate, and have sex with her when I was back. We were home for 3 days and she was the happiest in the world.
Now sex for me has always been delicate. She's the second girl I've ever slept with, and first in about 6 years. It was a big step for me emotionally.
The Friday before her graduation, she was really distant. That day she asked me to meet her at a beach, and I did. She was again super distant, and she started crying and said she couldn't handle a relationship now that she was moving to college.
Typically I bounce back fast from relationships, but:
1.) no one is home for the next week. I took this time for her, and all my friends are out at college. Every empty day is reminding
2.) the sex. I feel used in a way. She begs me for sex, gets what she wants then leaves me.
And of course I still love her. This is the first time a breakup has hit me like this, what should I do? So far I haven't told her any of this, I was mature and told her that I wanted her to be happy.
TL;DR girlfriend told me to take leave to see her, she broke up with me on 3rd day, I don't know what to do.


Source.