Hi Nat,
I'm dealing with the same thing from my ex but the difference is we met after his first deployment and he started shutting me out about 3 weeks before his 2nd deployment about 2months ago. He told me he had so much going on and he just needed time, he felt numb. He shut all his close friends out and started turning to "new friends", such as a much younger woman (17 years difference) who was also deploying. He denied it of course until I had physical proof and now has completely shut me and everyone of his friends out who caught him in this lie. I'm sure the embarrassment of all the lies and being confronted with it. He just isn't the man I knew just 2 short months ago.
He had never shut me out before so it was extremely hard for me as well. Especially since we were so completely in love with each other up until the night he woke me up at 4:30am to tell me he couldn't sleep and was feeling really stressed. He woke up the next morning and that was it.........complete shut out!! I believe it had to do with the upcoming deployment and also this girl. I believe he found comfort in her because they were both going to war. He would contact me here and there and wanted to see me before he left for his 3week predeployment training, this was before I knew about her. He contacted me during his predeployment training all the time, I think he was so miserable there he needed me because he couldn't talk to "her" while they were both training. Then when he returned I heard nothing.
I know the shut out is hard but just give him the space he is requesting and don't pressure him. Sorry this became longer than I planned but I just want you to know you are not alone!