Merry F'in Christmas - I want a divorce.

[limey]

I agree with those who say don't communicate to your son your feeling that it is the end of the world - whatever a kid grows up with is "normal" in their book, and it's best to treat it lightly.
Most of all - DON'T involve your son in ANY WAY in the negotiations/discussions/battles with your wife - EVER. Even if she tries to draw him in, get him on her side or whatever (and that can be very difficult). If she tries that simply stonewall with "That's between your mum and me, and we both want the best for you. Now, let's go play ball (or whatever other distraction)". Stay in touch with him whatever else happens - that'll count in the end, more than any explanations of how crazy his mum is ...