First, let me say that you have shown incredible strength through all of this and now continue to do so even as the blows keep coming. I have no doubt that you will not stoop to his level and you are capable of handling this in the best way possible, with the help of all the great advice found here.
He is just sinking further to his rock bottom. You are right, this affair is completely illogical. They usually are. If I was a betting man, I'd be willing to wager this relationship does not last through his deployment. Long distance relationships are extremely hard to maintain, especially when they have no foundation. Not that any of this really matters, but the point is it's just another distraction for him to run away from reality and his problems.
Stay strong and make sure you do what you need to protect yourself. Continue to maintain boundaries and maintain your dignity, be the better person. As I mentioned before, he is walking a fine line if he is willing to commit adultery and arm you with a written statement of intent. Go to the Air Force base, they will help you out (my W is Air Force).
M: 26 W: 26 M: 1.5 T: 3 No kids BD: 31 March 2018
W's affair began: 23 March 2018 Affair confirmed: 18 April 2018 Confrontation/claims she ended A: 14 May 2018 Ended in-house separation: July 2018