Please do try and accept the status quo, op. You'll feel better if you do and there's nothing you can do about it if you don"t! It is what it is.
As I said in an earlier post, you will inherit when your mum dies and I'm sure she does appreciate you.
You talked about your brother being useless in this scenario. There are people who just cannot cope with doing intimate care for relatives, it's not their fault and they can be men or women. I know this, a cousin of mine couldn't bear the thought of (for example) cleaning up her mother when she was ill, it made her feel ill. She didn't want to be like that but that is how she was (she found dog and cat poo difficult to deal with, and vomit). We are all different.
I'm quite happy to care for someone but it's not because there's anything special about me, it's just how I am. There are plenty of other things I can't do, the list is endless!
It strikes me that you care very much about your mother and you do what you can. Please try and get some sort of comfortable fold up bed for when you have to stay, not an impossible task. Ask around in shops that sell such things.
Leave any resentment behind you, it's not worth the anguish you are causing yourself.