He should be putting you and his relationship in your shared home first and his kids should be fitting in around that
Why? Why if this is not what he believes in? If his approach to life is that his kids come first, then that's his right and he shouldn't have to change his parenting views for someone else. Where he went wrong is when he decided to start a serious relationship with OP if she showed signs of not accepting the situation from the start, or not end it when he realised she would never accept it.
When I was single, I made a promise to myself and my kids that no man would change me who I was as a mum. I was confident in the way I was raising them and as a parent it is and will always be my right to do so as I wished. There is no right or wrong way to bring up children, different views resulting in different adults with different upbringings. For the most, these adults do just fine in life.
When I met my partner (who didn't have children), we both agree that it was essential that we were on the same wavelength when it came to my children. For him, it was important that I was raising them with similar values to those he agreed it, ie. if my kids were brats (in his eyes), he knew that it would not work and there would be no reason to develop our relationship further. In my eyes, it was essential that he understood that my kids would always come first. He totally respected that and agreed that how it should be. He himself was raised by a single mother who always put him and his sisters first.
What annoy me in threads like these is that both adults get together with their eyes closed, ignoring issues that got in the way of building a totally happy relationship together, and then once the relationship is well established, decide that it isn't fair they should have to face these issues. How can you say that a partner is perfect but for their kids? It would be like saying that a person is perfect but for their nationality, or perfect but for their past education, ie. the things that make them who they are in the first place. When you get together with someone who already has children, you need to appreciate that there is much more to consider committing to the relationship than there would be without.
If you get with someone and you don't like the way he brings up his kids, don't just assume it will get better, run a mile before you commit, it will be easier for everyone in the long run or accept that this is how it always will be (as ultimately, it always is).