I cant cope anymore D=?

So about 2 years ago my grandads operation went wrong and he was in Intensive Care Unit for a few months with cancer and blood poisoning, and now he has bronchitis and has has blood in his poop (he has a bag) so they think his cancer has come back. Im 15 now and I HATE seeing my grandad like that, Im studying for my GCSE's and exams aswell as practising for some horse shows this year, My mum is so down when things like this happen as she hasn't lost much family and she cries so much about if he or my nan died. I love my grandad so much and he spoils me but my uncle treats him and everyone like s'hit and takes his money, makes my nan work and do his cooking, cleaning and everything for him. I really cant cope at the Moment because i want good grades but i want to be with my grandad incase this is it. How can i get through all of this and cope with my grandad? thanks :)