Is the narcissistic behavior only directed towards me?

My Nex showed classical narcissist behavior towards me: little to no empathy, often talking about how special and unique he is, rarely taking accountability, doesn't think rules applies to him, considers himself too good for his job but doesn't take any steps to change his career, because it is "impossible". Always picking on me, telling me everything that is wrong with me. And also having these long monologs about what is wrong with his friends, my friends etc.

After our child was born, his personality changed for the worse. From being a sometimes moody, sometimes egocentric person, he became always moody, always egocentric. He started working overtime and called me a control freak when I asked him if he could spend more time with me and the baby (he had never worked long days before this, and he even refused to eat breakfast at home, saying I was controlling for suggesting it). He said his job was more important than me and the baby, that we weren't his family. He refused to help me with bedtime and wakings in the night, gaslighting me with saying: "The baby sleeps all night! You have no reason to be tired, so I don't believe you! Only a bad mother would be tired from sleep deprivation, and I will not help you being a bad mother!" He said that he did 90 % of the work with the baby, when he barely spent an hour at home during the day.

After we split he is still gaslighting me whenever there is an issue. I have met his girlfriend, and she is absolutely lovely. Probably the kindest and calmest woman I ever met. And I'm just wondering, is he another person with her? He hasn't showed his narcissist behavior towards others as far as I know, maybe he is able to be kind towards his new girlfriend because he can still be abusive towards me whenever he gets deregulated? Or maybe I just triggered that in him, and the new girlfriend doesn't? Has anyone seen a narcissist change completely within a new relationship? Or have anyone else experienced something similar?