I think it throws them off their game a bit to see that you are not falling apart. They feel that they are the ones walking away and we can't make it without them. Sometimes we have told them that, so they must wonder why we are doing well.
Yes, it would be good if they could see the extent of the pain they are causing but I also think that in their honest,alone moments they feel pain. They immerse themselves in distractions so that they do not have to focus on the pain.This is why they get a new, busy, non- stop life.