Losing my dad

My dad had a cold at the start of March and went to the doctors he sent him home with antibiotics but it got worse he ended up in a&e they drained 3 liters of fluid off his lungs 

They tested the fluid and found cancer cells ,after a ct scan they found it  has spread through out his body and have given him 3-6 months 

My dad was genrally of good health he never complained about  being sick . My heart is breaking I feel so useless although I'm a 48 year old Male and my dad is 74 I don't know how to cope I've  never lost any one close 

I'm  not sure I want to see him slowly die , I feel I have to be the strong one because in the only son with 2 sisters , but I'm not 

What can I say to him when I see him ?? , i didn't  leave home till 45 we were all  so close , I love my dad so much

Thank you for reading this I know I'm not alone but I feel so sad