During my mother's first year with us, my husband was resentful. He was never one to seek out my companionship, but when he saw the time I was putting into my mother, he grew annoyed that he was never included or that we could never do anything by ourselves any more.
If you can, perhaps try to have a dinner out with him once a week, having a friend or neighbor or sibling in to be with your mother. Aim for a weekend away once a month, or arrange for a holiday where you can have two to three nights alone by yourselves doing something you both like. It's not cheap, but you need some respite with him so you both can sort out what will work and what isn't working for him.
My husband "came around" after about a year. I think what happened was his family and friends told him how generous he was to do this, what it said about him as a man, what it said about the strength of our relationship, and so forth. He is so on board with this now that he helps me by taking her on, on some nights (because while we have daytime help, we do not hire overnight help), so I can sleep. It has been a total turnaround, in other words.
I think several people on here have not shown the compassion you had hoped for, and I'm sorry about that. We all speak from our own life experiences. I have been where you are, and it hurts tremendously. With a little bit of one-on-one with my husband and some built in dinnertimes by ourselves, we repaired what was going wrong and worked out how to move forward. I hope you too can find a place where you can reach through whatever screen he now has installed between you, listen to his anger and upset, and open the door to a future where you and he and your mother can live amiably together. None of this is easy. I feel for you.