I know how you feel. When I was in my early teens my 3 yo cat suddenly went missing. I posted flyers all over my neighborhood but got no replies.
Three months later someone found her across home. I cried when I saw her, she was extremely malnourished and emaciated and had been living as a stray. We figure she climbed into the open window of someone's car to have a snooze.
I had her home for less than two weeks when we realized something was very wrong with her. She was not herself and her breathing was labored. It turned out she'd been hit by a car and had internal injuries. She died shortly after successful surgery to repair the damage. It was just too much for her little body.
I was never able to say goodbye to her and it haunted me for a long time. I eventually had a dream about her where Missy came out of a bright light to say goodbye to me. I hugged her and cried and she purred and cuddled into me. I told her I loved her and watched her trot back toward the light again. After that dream, the pain was a little better. Sounds fabricated and cheesy but it really did happen.
Now, 20 years later not a day goes by that I don't think about her and miss her. For years I couldn't look at photos of her, it was too painful. I still dream about her often. In my dreams she's a friendly ghost who comes back to visit.
I don't know whether this is just my mind's way of coping with a significant loss or whether this ghost is real. But I swear I can some times feel her with me. I also once visited a psychic who once told me that my white cat sleeps on the end of my bed every night and that I should talk to her more. I never told this psychic that my pet was a female, white cat, only that I'd lost a dear pet that I missed very much.