Grieving the unexpected loss of my cat

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My 4 year old cat got into a fight with outside cat and died the next day. We don't know what happened. She had no external injuries and the vet told us she was just in shock and will be fine tomorrow. But next morning she just gave up on life within hours. We took her to the hospital and the doctors tried their best but it was too late. I am devastated and so much in pain. I don't know what to do. She was my cat and I got married 6 months ago. My husband was so nice to her but always felt he was a little jealous of my relationship with her. I don't know why but I blame him for her death. Like why didn't he take it seriously right away took her to the hospital. He said he thought she will bounce back. I know it's wrong of me to blame him but this incident is putting a strain on how I perceive him. I don't feel like being close to him. I keep thinking maybe if I didn't marry him or relied on my instinct my baby would have been fine and alive.