I lost my 3months Old Cat

I lost my cat of 3 months and i can’t stop blaming myself i think i am the reason for her death though i tried so many things to save her but there are so many ifs i took her to vet she got better but i don’t know what happened she just lost her oxygen than again i took her to vet but she died there and i did every possible thing she wasn’t eating anything i did force feeding i nebulised her after every 8 hours(told by vet) he didn’t gave me any medicines to give to him he just used to give him injections he told me that my cat possibly have pneumonia and diarrhea. I thing what i did wrong is that i didn’t force feed her enough i just want to die i lost him i lost moon