It is so great that your son is talking to you about his feelings. You are doing a good job. My heart breaks for these children as well. My son is 16, my exAH moved out 2 1/2 years ago, and he lives only 30 minutes away but makes no effort at all to have a role in his son's life, other than occasionally demanding that I bring our son down to see him.
My son is such a quiet, smart, sweet kid. He holds all his pain inside. It's just the two of us now that his sister is away at college. I do feel your pain.