I know what you're going through. Last year my cat I rescued that I had for 4, almost 5 years passed away. I was devastated for lack of a better word. I just kept in mind that she's in a better place now. This is a bit embarrassing(lol) but I would imagine her in a sort of cat heaven, playing with other cats. It's a bit goofy, but it helped. I also kept in mind that she will never leave my heart, and that I would always remember her. Lastly, I often remembered all the good times. Hope this helps, I know it's very tragic to lose such a close pet. :)
