A little update from the original post:
I wrote a letter and read it to my girlfriend in person when she visited. It went over very well. We are going to start writing letters back and forth as a way to feel better connected.
I also had a long talk with her about all the concerns I mentioned in the original post. I DEFINITELY feel better having talked about everything fully. We talked about long term commitment, daily communication, trust issues with other people, honesty, and trying to be happy despite being temporarily apart. We were on the same page about pretty much everything, and are compromising in the areas we are not.
If you are in a long distance relationship I definitely recommend taking the time to go through all of your wants and expectations with your partner and let them know if you are struggling with things. I can tell you I feel much better. Because she has been such a major part of my life for so long, it's going to be hard to work on feeling happy and fulfilled when she's not around. BUT - If you are freaked out by worries that you haven't fully talked about - it will drive you crazy until you do!
Also I would say don't leave anything left unsaid. I was fairly certain that my girlfriend and I were on the same page about commitment, etc. but I felt so much better laying it all out there and hearing her lay it out as well. This is what is working best for my situation anyways - when we have been together for a long time and plan to make it through a set amount of time spent apart.
Thanks again for all of the helpful advice! I hope if anyone else is going through this, the comments and stories here will help.