why do i feel nothing

i just got the news that my mum who has terminal cancer is going to be having the last months of her life now, everyone around me is sobbing horrifically and i haven’t shed a tear since her diagnosis, i feel so guilty for looking like i don’t care. i also find it extremely hard to talk to her, we used to be so close before her diagnosis but i can’t talk to her now like we used to, i know im gonna regret that but i just physically can’t do it. im scared that when she dies im still not going to cry and im going to look like a terrible person, does anyone have experience with this? ive never lost anyone in my life before this so i dont know how im meant to be feeling. im sorry if this is the wrong group to say this on