Oh love, it's like you're the Invisible Woman, isn't it? You keep talking, asking for help, but no-one is bloody listening, because it doesn't suit them. Aunts just want to preserve the inheritance. GP can't be arsed. Social care just want you to shut up and carry on, because it saves them money. Housing association - God knows what her bloody problem was.
And now you're having a nervous breakdown, which has been clearly building for months. If anyone had bothered actually seeing what was going on in front of them, this would not be happening.
I'm so sorry, you have been badly let down, by everyone. And now you're very unwell, far too unwell to carry on. The symptoms you're describing are those of a proper breakdown. You need help, and you need it fast.
As a pp said, as long as you keep doing what you're doing, no-one is going to help. The situation suits them, even though it doesn't suit you, or your granddad. He is far too ill to be being cared for by a single person, who is mentally unwell herself. No matter how hard you are struggling, you won't be able to cope at all much longer.
So please. For your sake, for your Granddad's sake, and for your mum's sake (do you really think she'd want it to be like this for you? Of course she had higher hopes for you than being driven to suicidal depression by other people's selfishness!) just say you're stopping. Make an emergency appointment with your GP today, then stick to your guns. You're happy to still see your granddad and spend time with him, but not as his carer.