Been looking after my auntie who had thyroid cancer and then developed a brain tumour, she's had it removed and is now in recovery but cant leave the house. My nan is also blind and suffering various ailments that come with being almost 90. Im lucky as there are lots of other family members to help out but what you're doing is incredibly selfless and you should be proud of yourself for doing the right thing despite the difficult circumstances. Watching someone you love suffer and caring for them can be really hard but you have to stay strong and try and be positive for both of your sakes. Remember that they wont want you to be upset and that you owe it to them to make sure you appreciate every minute of your own life as fully as you can. Sorry to hear about your situation anyway mate, just keep your chin up and the fighting spirit alive, thing WILL get better.
Keep your chin up mate, I have been through some rough times myself but you learn from it and it makes you stronger, try to keep a sense of humour it helps. :good