Sorry to hear about your loss. I feel you as I also lost my cat when he was still young, only 6 months old.
I also feel that he could have lived longer and I could have done something to prevent his passing, I'm guilty and troubled even though it's not fully my fault
that he's gone now.
In my case, my cat Miming was hit by a car and I couldn't do anything to save his life. I love him more than anything and I also denies the fact that he is gone.
It has been 2 weeks now since he passed away, I still about him every single day.
Wishing he returns and purr again between my feet. I miss holding him in my arms.