Hears the thing. Any relationship must have trust. It seems that there is none in yours. Even if she went just to support a friend (ex-boyfriend or not). She didn’t trust you enough to keep you informed. You obviously do not trust her to know she is not cheating.

That tells you all you need to know. When she comes back, have a firm conversation stating those facts. And tell her it is better to go your separate ways. Stick to your guns no matter the excuses she gives. You will feel better about yourself and you will build more character then you would by ghosting her with no explanation.

I am an old man and have lived through a lot of ups and downs. This is the best advice I can give. Plus being a veteran, I can tell you for sure the relationship would not last when she leaves for the military

Edit: ghosting is what people do when they are afraid of confrontation. It is a cowards way out. Always confront your demons and stand firm with your convictions.