boyfriend going through grief

my boyfriend's uncle is dying of a terminal cancer and hes been sad about it for the last few days, but i don't know how to help him. i've only dealt with the death of a relative twice in my life but i hardly knew either of the people so i wasnt as affected by them. i want to help him, even though his uncle isn't gone yet, its inevitable and it seems that itll happen sooner rather than later. does anyone have any advice for helping him through this tough time? i just feel so helpless