Hang in there praying! I know the feeling of thinking how could someone that you love so much and had loved you back for so long, suddenly just not care or even want your love. It doesn't help when all around us we hear the platitudes about "You only get the love back that you're willing to give" and such but there, right in front of us, is this person we love so darn much and they just don't care. Hard, I know. I think that what made me really understand that this wasn't about me was when my W went from saying she would never put her kids through the pain of D like she went through as a child to "We all all hurt our kids, they'll get over it".
If it truly was about the M, then they wouldn't also turn their backs on the kids as well, no matter how "bad" they thought the M! I know how the sitch with the kids hurt's so badly. I have 2 girls, one who, at 14, really needs her mother there to help her transition into the woman she is becoming but can't count on her mom at all. I also can relate about the in laws "helping" him when the last thing he needs right now is someone 'helping" him do all the wrong things (in my case it's FIL).
If showing them how much we loved them and cared about them was the answer, most of us here would easily get through this and have great M's. Try to see that if it was really about you or your M he would still be the great dad he was before. Try to stop being "shocked" or upset when he does things like not care about his son's wanting him to go to his meet (something I also am still trying to stop doing so I know how hard it is!).
The best thing for both of us right now is to detach from our S and expect nothing. Make sure you get the best possible terms for yourself and your kids if he insists on going forward with a D. Try to see that he is no longer the loving dad and husband you remember, that person is gone and may never return (I know how hard that is, believe me)and in his place is this selfish stranger who you need to protect yourself and your kids from. One good thing about his going into the Navy is that he won't be able to get out of paying to support his kids so make sure he pays his fair share in any D.
I know you're hurting now but I can tell you are a good person with much to offer the people in your life and the world at large. You WILL come through this and when you do, you will see that you were the prize all along and if your H couldn't see this he is all the poorer for it. Some day he may come out of his MLC fog and realize just how much pain and damage he caused the people who loved him the most in this world. When that happens you won't be the person you are now but a better one whom HE will need to prove HIS worth and value to before you let him back into your life! Until then, know you aren't alone and we all are here and rooting for you.