I think the fact that it has just been a few months may be in your favor. Time has a way of taking all of us through troubles waters.
Also the fact that blowing up is often your son's pattern of behavior may suggest that it's temporary. If so, doing nothing may be the wisest course of action.
A marital split may seem to even an adult child like an inner split and a need to choose one parent above the other. If your son reflects behaviors that he learned from his father, he may interpret your decision to divorce, as rejection of him on some level...(perhaps unconsciously.)
It's always so much easier to blame others than it is to see what's going inside us. He may think his wife is going to learn something from the choices you are making and leave him. Who knows?
Again, a lot of guessing going on here but it is my guess that his rage is on top of a lot of fear and that your DIL is going to "lay low" and ride this out, if she is a meek person. It would be nice if they could see that it is your issue but I'm sure that seldom happens. It's probably idealistic to think otherwise because such a radical change usually affects everyone.
You have taken a stand and now you are finding rejection when you need understanding. You can't change your son's reaction. You can only try to understand it...wait and hope.
You may also find seeing a counselor as a good idea. Think about giving yourself an advocate and some much needed professional support and perspective.
Bless your heart.