What should i do to stop crying?

my grandpa only has 3 weeks to live and i cant stop crying my mom said " he will be in a better place " my brother said " its ok if he can fight in the world war 2 he can fight this" he has had 3 heart strokes and and i been put back in the hopstital he cant talk or move but when he saw me my mom and my brother he tryed to smile and nodded hes head this is my great grandpa and it happend just a day before my great grandmas birthday witch makes me evan sadder and i just wanted to know if anyone could give me advice on how to cheers up a little.....?