I've had to endure the loss of a pet and companion when my cats have died over the decades, and it really hurts. They become another member of your family, and it can be gut wrenching watching them suffer before they finally succumb and are no longer with us.
In August of 2020 my older sister died after spending a month in 2 different hospitals, she was barely 64 years old. Less than a week after her passing, I lost my cat MOLLY to a congenital heart condition. She was less than 10 years old at the time. I think I cried more after losing MOLLY than I did for my sister's death. MOLLY was the perfect companion for me, I had to retire and go on permanent disability, which meant I was at home by myself all day while my wife was at the office. She kept me company like she was a dog, she'd just hang out with me inside or outside the house, and always did what she was told. She never wandered off or went into the street, and loved sitting in my lap. I still miss her very much, and my suggestion to you is to adopt another adult female kitty to keep you company. It won't make you forget about your loving kitty Marina, you get to keep those memories.

Here's something that helped me a lot when my beloved dog died.

so sorry for your loss. it's a loss like no other. I have been there too many times to think about and I remember them all because they live in my broken heart. HUGS!!