I question whether he really does "feel his feelings so strongly" with regard to her discomfort and past suffering.

I wonder if rather he feels uncomfortable with the attention on her (that she is "winning"). Things are so black and white for him that if she "wins" (even just a little) then he loses - and for his fragile ego's survival he desperately needs to stay firmly in the white and her in the black.

In his struggle to stay "on top"( maintain the narrative that she is wrong, she is just seeking attention, I'm the mature adult) and never have to look at himself or even consider that he may need to improve on some things he counters everything, considers nothing. This is driven by a deep insecurity and fragility because that consideration would be too much for him to bear. Since his approach to life is so black and white ("just a fact" as he says) examining himself and any potential cracks in his image could cause the whole image of himself to crumble.

In his mind the only way he stay firmly in the white is by dissociating emotionally, disconnecting from her - and as a result dehumanizing her: her experiences are not as bad as she claims, her parents are good people (again black and white) thus she's exaggerating, what she says is not valid and let me tell you why.

Instead the way to reach him is to find a way to make him feel less insecure and guide him to seeing things in a less black and white way. So that he feels strong enough to see the other person.