this may not be helpful, but I wonder if trying to keep your husband's spirits up is a waste of your energy, and counterproductive to boot.
Before we married, my husband's daughter was a real bone of contention between us. Well, actually, she wasn't: the way he treated her was. I can see real parallels in the situation. And we parted many times during our courtship over this issue; right up until the time when I was so tired of it I told him that, if he didn't change his ways, he would end up an old man sitting in the corner smelling of wee.
I think the image helped. Not saying we have never revisited these issues - they have always been a source of tension - but I could never have married him if he hadn't recognised that he had to be the adult in his relationship with his child.
Oh - and I'm also reminded that I told him of all the cases I'd seen of children enduring truly horrible childhoods who still just wanted to be with their parents: knowing that it's really, truly difficult for your child not to love you was the other side of that.
But that was early in a relationship and we had a chance to change the habit of only a few years, and make a new habit. By now, you are so right - you can't change him. Looks like he's made his decision, as you say, for whatever reason. His daughter gets what she wants; but it's fairly easy to predict that by the time she gets it it won't be what she thought it was.
And you are strong and you will be strong, you have faced up to mistakes and are changing things. 52 is an excellent age to be starting again.
I wish you lots of love and light.