I fully understand your situation. I won't even tell you how long it's been since my xah has seen his kids or how little quality time he spends with them when he is lucky even to have them want to see him. Why? Because in the grand scheme of things, it's kind of irrelevant.
It's as Mr. Christian said. Expectations do bring resentments and I've learned not to expect (or even have any misguided hope) that my x is going to change anytime soon. He's proven to the kids by his repeated behavior that this is how it is and they (like I) eventually just had to come to terms with it in their own way.
Yes, I know that sounds harsh, but really - there was nothing for me to do. I'd enabled him and covered for him for far too long and when I learned to let go and mind my own business, they had always seen and known the truth but my letting go and staying out of it allowed them to come to terms with it. And that is something that I couldn't do for them no matter how much I wish I could have made things easier or better for them. I couldn't/can't change him - that's just a fact. I don't have to like what he does or doesn't do, nor do I have to approve. I chose to go on with my life and that meant allowing him to be who and how he chooses to be.
As Glass Prisoner said - someday he will regret his choices. But there again, there is nothing you can do about that.
For future reference, let me just give you a forewarning.........these feelings will stick around, or reappear, when another woman enters into the picture most likely. (I'd seen it before and it's happened w/ my own situation as well) So I really hope that you'll find a way to digest and accept the reality here.
He's not a great Dad - and may not ever be.