I wasn't a Ranger girlfriend, but I was an Army girlfriend for about 3 years.
My ex (the military had nothing to do with our break-up) and I started dating before he went into the Army, so I was with him through basic, training school, and everything else. I can tell you that the waiting was very hard, but it made the few minutes of talking we did get to have all that more special.
When he came home from training we got engaged and (though we didn't know it) had about 2 months together before he got his orders to go to overseas to Iraq.
I lived in a constant state of worry, not knowing if the last phone call I got was going to be the LAST phone call was the worst. There were a few times when we would be in the middle of a phone call and the line would just go dead, or he would just have to rush off with no reason why.
Looking back at it all now no matter the stress of the relationship, everything was worth it. The time we had together (in person) was fantastic and the time we had apart (while he was in training or overseas) we would joke about being the "appetizer for our main course".
In my opinion, every relationship is hard, military ones just have that extra stress level added. But to be completely honest - if you really love the person, think you see a future with him/her, and are willing to do the work (whether it's having a Skype date every weekend instead of the real thing, or go to sleep with his tee-shirt instead of him every night) go for it! How many chances are you going to have at being happy, and if for whatever reason it doesn't work out, you have great memories to look back on.
You are only the person you are because of the experiences you have. I am now the happiest I have every been with my boyfriend, and it's partly because of my failed military relationship. Being in a relationship where you spend most of your time apart teaches you to really truly appreciate when the person is there.
I hope this answer helped you - good luck and, trust me, it ends up worth it, no matter the outcome