Mum is dying

My mum has been diagnosed with pancreatic cancer my stepdad told me today that she has a year if lucky my mum didn’t want me to know, I am being really brave when I’m with her but absolutely broken when I’m not with her, i am so scared I am not going to cope, I have two children and a grandma that I despise because it should be her turn, I know that sounds awful but gran has been ‘dying for 7 years ‘ but modern medicine has kept her going, I lost my brother 7 years ago suddenly from sepsis, my dad had a breakdown and has never come back from it, me and mum are so close she is my best friend my mentor my everything and I cannot imagine a world without her, how can things turn out so cruel ?