Hi, itm, I know it just destroys you inside when you see how their R has deteriorated. It hasn't been all that long since all this began, has it? When the SHTF here, my H made statements that it was only his feelings that mattered now, and he didn't care at all whose feelings he hurt, even our S's, and that he was doing something GOOD for himself, now. Crazy a&& talk. But, he eventually came out of it, and I don't know how much of it he even remembers. Once when I reminded him of what he said about S's feelings, he denied saying it. So, maybe your H is so far into his darkness, he just doesn't realize how bad he IS making things for your S. For him to just continue on as though nothing has happened, shows this.
I agree with being open with kids. I have always been with my S, and now he is 19, he is still very open and honest with me, and knows he can come to me at any time to talk about anything.
Like you said, take your time, discuss it with his C.