He cheated because, due to the circumstances of your being apart for so long, you are not able to fulfill the marriage acts that help hold a marriage together maintaining an active sex life. He is away from you, and not able to be intimate with you, and as the bible says, this leads for satan to get a way into a marriage.
I'm not saying this to put you down for your choices. Just pointing to a truth. This seems a pretty common issue among military couples. The women are at home, alone for months or even a year at a time. They become lonely and eventually they succumb to this loneliness and cheat. It is just the risk of a marriage where the couple is apart for long periods of time.
As for what you can do? Well, it depends on his feelings towards the issue. If he is full of genuine regret, then you have the chance to reconcile and keep the marriage together. But for this to work you will need to understand that you both entered into a set up which was not good for your marriage. Not that you both share equal blame. He does take most of the blame, but this is a situation put into place by two people agreeing to it. And by doing this, not taking the bibles warnings on how to handle marriage. You both may require some marital counseling and likely have to see if he can make changes in his job that doesn't require him to be apart from you so much.
But if he isn't bothered by his actions, there's not much you can really do to change his attitude. And he will eventually choose to leave or stay and try to make it work. Or sometimes they stay and continue cheating. It all depends on the attitude he has towards his behavior.
