Echoing the let the dust settle sentiment. Give your son what he wants right now, even if it is painful. He wants to be left alone; grant him that. He is going through exactly what you're going through - something that is out of his control that he does not want. Allow him to react, and try to understand that is what he is doing.
Do whatever you can to separate the two in your mind. Your husband abandoned you, yes. That's a valid feeling and you have every right to be upset about that. You have a right to be upset about your sons actions too, because he doesn't understand the full picture. He's not abandoning you, though, so try not to look at his actions in that way.
He's dealing with something hurtful. Let him work through those feelings.
You mentioned that your daughter and he talk about things. Don't pressure her to plead your case - I'm sure she will do it naturally. However, let them continue to have that relationship because he will begin to see that it's not just you. And, unfortunately, you know that your husbands true side will come out. He's going to need another doormat (that's how they treat us). He may be the fun, laidback dad right now, but he's no longer got someone to tidy it all up for the kids.
Do your best to keep in mind that your son is going through the same rough time as you, and is dealing in his own way. He gets to do that. Be prepared for when he sees his dad for what he truly is, though, because it's going to happen.
Kids take sides in divorce, especially when they first hear of it. Everything will settle, though, and you will get through this. He will get through this. You'll get the opportunity to mend this relationship. It will be hard for a while, but keep yourself from letting these negative thoughts hold you hostage. It's time to start healing.