Girlfriend left after 6 years, After i enlisted in ARMY

So my girlfriend of 6 years just up and left after she totally supported me in enlisting in the army. I feel so betrayed and don't know why she'd do this. I did find out about 6 months ago there was a another guy for a little so its not so sudden shes been thinking this i guess. Now on the rare occasion we talk she never has anything to say, her feelings seemed to disappear. Any suggestions on some closure? I leave in January and really want some closure before i get sent off to war. She's always on my mind... i just want to be happy agian. Thanks in advance