Late to this, and I haven't read all the responses, but one thing sticks out, so...
To me, it is eminently possible that they never discussed you - your existence was - please excuse the expression - the gorilla in the room, the main piece of reality that absolutely proved they were effing up and living in a fantasy world. If they acknowledged you, they also had to acknowledge how foully they were behaving.
Passing a poly and coming clean on most other stuff - he really could be telling the truth here.
You've shown a lot of courage and insight in your posts. You know yourself a lot better than I do, but please at least consider the possibility that, if you feel pain, the pain is really there. I say that because my experience is that the amount of pain seems to have been way, way more than I expected.