Decide together whether you want to tell your son seperately or together. In my case, since I wanted to save the M and W wanted the D, I told her I couldn't do it together, because it would look like I agree to breaking up the family. On the other hand, after she told the kids and was truthful with them that it was her choice and not mine, it still drove me a little nuts what else she might be telling them. Just a consideration.
As far as D goes, I insisted W do all the work, so she got a lawyer and filed, then I got one and responded - it costs more this way, but it's only money. The vibe I got from her is that she hated that I was not "cooperating" and was very, very cold and irritated. But she's still getting what she wants - to not be married to me.
Right "now" your W does not want to be married to you, and either way she can legally attain that objective. So decide how much you want to cooperate. I tried to buy time, in the hope that W might have doubts about D, but it didn't work. However, in my case there is an OM involved - that's a huge factor or "crutch" for my W. Her WAW syndrome wasn't even triggered until OM came along.
My advice is do not do anything with the "goal in mind" of winning her back - that's way, way down the road and possibly even a dead end. Make you goal the best possible life you can give your son and YOURSELF, accepting the possibility of different future scenarios.
Make it clear to her that you believe you can still have wonderful M and the best envornment for your son is a loving home with a mom and dad in love with each other, but validate her feelings.
Only then can you give her what she wants - the D - or she'll take it kicking and screaming - or she may even have doubts about the D. You know her best. Do what's best for your sitch; there are no magic answers.
Me 53 XW 50 M 18 Years +2 S14 D19 Bomb 10-24-10 Served 1-27-11 Mediate 4-21-11 Civil D Final 6-2-11 No church anullment "A man is not finished when he is defeated, he is finished when he quits."