I'm so sorry that your son is having such a hard time with his dad. I'm in a kinda similar sitch with my H and 3 kids. My youngest (D8) would light her hair on fire at this point if she thought it would get her father's attention. Of course, he doesn't recognize any of it.
In the last several years, as my H has been going through the early part of his MLC (I believe him to now be the poster child of MLC) he has stopped being a co-parent and has been dependent on me to nurture his relationships with our children. Well, that is the one thing that I have been really able to do since bomb drop - not be responsible for his relationships with our children. They are smart enough to see what's going on and who is here supporting them, and who is around only when it suits him.
Hang in there and know that your boys will pull through this, even if we don't like that they have to struggle at all.
Me: 42 H: 44 M: 17 1/2 T: 19 1/2 S: 14 D: 10 D: 8 Dog: 16-17 (very old & H's responsibility, live w/ me) 1st Bomb (I need space): 2/3/12 2nd Bomb (ILYBNILWY): 2/11/12 Moved out: 2/12/12