He is doing exactly what my friend’s XH did to her eldest daughter - instead of centring the child’s feelings and trying to ensure he made the best of the situation for her sake, he was a totally narcissistic, self-absorbed man baby and pushed all of his shit onto her, making her feel responsible for his emotional wellbeing.
It’s a truly awful manipulation tactic, because the aim is really vindictiveness towards the absent partner (he wants the kids to see you as the bad guy who’s hurt and abandoned daddy and left him all alone), but the net effect is that the child feels simultaneously responsible yet helpless. They can’t change the situation, so instead they worry continuously about the ‘sad’ parent, even when they’re not with them, and it leaves the child in a permanent state of vigilance and distress.
It’s psychologically incredibly damaging to kids who are being emotionally manipulated and squeezed like this. My friend’s daughter, now an adult, suffers from anxiety and an eating disorder that’s ravaged her, mentally and physically. She’s been effectively subbed in as her father’s keeper from a very young age and has been unable to escape that dynamic even in adulthood. She sees him as a victim, and it’s caused endless problems between her and her mum, whom she blames for the whole situation, even though she can rationally see that her father was a horrible husband and parent.
Get therapy for your child asap, and ensure the therapist knows about this issue and can try to help protect your DD from the consequences of his selfishness.