I need some advice I'm having a difficult time?

I am 17 and I was wanting eagerly to join the United States marine corps. I had a girlfriend of two years she promised everything would be great at first and then just yesterday she confessed to me she felt 4 years was too much. I do understand that but in this situation she had promised me she would wait. She would show me pictures of couples she wanted us to resemble when I got back. She always told me she was loyal and in the last minute where I needed it to count she said to me she wanted to end the relationship. I did I wished her the best as I do love her she was my princess and I'd give her anything for her to be happy. Although to my surprise she would be happier if we broke up. I feel I miss her but I don't want to get back together if that's the kind of loyalty she really has. I just need at the very least some advice.

I would want her to be happy and the thought of seeing her again is almost unbearable. I feel ill burst into tears she is to me what many call my puppy love