I keep thinking if he really did love me why would he shut down?
Don't even go there. It's not about you.
While I have no idea what he is going through I do know what I experienced for a while. And one of the books I read said it something like this. There is a war going on. It's not that he is in the battle field, he is the battle field.
I had competing thought patterns happening. And while I didn't trust the emotional side it was winning a lot of the time. Forget about logic. Just get out of the way. You could so easily be cast as the enemy. And you won't know why or what you have done. Being supportive is good. But sometimes you need to recognize that there is some crazy shit going on that you have no control over it.
This was some of my experience. I don't know what goes on with other people. So take it with a grain of salt.