Why our memories could last long?

I have a cat named Coffee, who has been with me for three years. The more time goes by, the more similar our personalities become, which makes us become best friends. But she died of illness in March this year. After she died, I was so depressed that I couldn't let it go. This project records all the happy and annoyed memories between coffee and me to thank her for the wonderful time she once appeared in my life.