I went through exactly the same thing with my husband when he came back from Iraq in 2003, he was a colour sgt while he was out there.
I was pregnant with our second child when he left, had me up on a pedastal always very loving, holding hands, cuddling etc. Sent loads of letters and seemed fine when he phoned home.
however was I in for a shock when he got home for the birth of our little boy, he was like you described your own husband cold, unemotional, wouldn,t say he loved me (not that he said he didn't love me either!) I remember the night after giving birth I took severe leg cramp and woke up screaming in pain, he sat up and shouted at me saying it was my fault as I had clearly not drank enough water which startled me as he'd never spoke to me like that, I lay crying as he went back to sleep!
He went back to finish his tour and came back the same if not worse, not talking, snippy etc I too thought my husband had an affair out there, though this isn't his charactor either. I even asked him, saying I could see why this could happen, during war, the preasure, thinking you could die anytime etc. He didn't do or say much to make me think otherwise simply said he hadn't but if that's what I thought there wasn't much more he could say! He even told my parents he thought I had postnatal depression!!
After about 4months of this I finally broke down and gave him the ultimatum he had to change or I was taking the kids and leaving, I explained how I felt and how he made me feel like nothing and unloved.
That night he finaly opened up to me, he spoke of the things that went on over there, how he couldn't cry when his friends were killed as he had to be strong for his men. He didn't want to tell me the stories as some things were horific but I didn't judge just simply listened to him. It was a gradual thing, he made more effort with us as a family and I was like his councillor someone he could talk to openly, none judgmental no matter what he had done.
It took a long time but I finally got my man back, only to be hit with the fact he was going back the following year, the dread was imence but he wanted to go back, I couldn't understand why either.
Thankfully it was completly different this time as the war was over, he still lost friends and still couldn't bring himself to cry or bring his guard down infront of his men but this time when he came home he was glad to be back with us and even laughed when telling me some of things they went through (army humour!)
Although I gave my husband the ultimatum it might not be right for you to do, you are the only one that can decide as to how you think your husband will react to this (I was fortunate as it could have taken a diferent course) what you have to think is, do you want to carry on this way or will it be better for yourself and kids to be away from your husband?
If you need anyone to talk please contact me, I was surprised to see I wasn't the only one to go through this, my friends all seemed fine and didn't talk about anything goinging wrong in there marriage, I felt very alone at the time too, hope it helps you to know there is light at the end of the tunnel although it may take sometime and effort on both sides you may still get your husband back to the man he was before he went to Iraq. Good luck and I'll be thinking of you