@Joseph13,
I'm sorry to read this - and I also thank you for serving.
The thing about serving in the armed forces is that it's like one big, long business trip. And that messes with the dynamics in a relationship, even under the best of circumstances. You also have a few major strikes against you - you are both young, and I am going to go out on a limb here and assume that you are each other's first serious relationship, you probably lose your virginities to each other, and she may even be your one and only.
Plus you have both already clearly had second thoughts.
I do hope you don't have kids. And if you don't, for the love of God, please use birth control every single time. Because bringing a kid into this screwed-up situation is really unfair to the child. And as for your sake, use a condom
every single time. She has slept with other guys. This means her sexual history is suspect and you are at risk for STDs.
Yeah, it's that serious.
I highly recommend counseling. Talk to the base doctor and get a referral. You will likely have to go by yourself, given where you are, etc. But when you are home, try to get her to go with you. I doubt that you can save the marriage, but it sounds like at least you don't want to give up quite so easily. I suspect that counseling will be more to your benefit, to give you tools for dealing with what is probably an inevitable breakup. But I still feel you would benefit from a talk and getting some help with the transition and also with how to deal with how life in the armed services can change a person and their preexisting relationships.