Your S13's reaction reminds me of mine when I was that age (and the oldest of three). I showed no reaction at all when my mother told me she wanted to D. I was, however, extremely upset. I just didn't show it to them. I was furious with my mother for being the one who wanted out. I really didn't care whether or not she was happy with my father, I just thought they owed it to us to stay together and work out their issues! I felt sorry for my father and the pain he was in.
Every time we did something as a family, I was hopeful that they were reconciling. It did $uck big time!
Good luck, TG--especially over the next week.
Me: 51 H: 52 T: 23 yrs M: 19 yrs S18, D16, S14 (special needs) PA: 2003/2004 Piecing: 2004 on Suspect H had EA: 8/2012-12/2012