I'm so, so sorry. This makes me very teary eyed. I know your pain all to well. When I rescued a Persian two years ago, I had only had him for eight months before he suddenly passed away. What makes it worse is there was no answers ad to the why of it. I too held him afterwards and I think about that moment often. But in a good way. I told him all the things I wanted him to know. I took comfort in all the things everyone here keeps saying: "at least he knew love from you while he was here. That someone cared deeply for them no matter how little the time was."
I did adopt again, not to replace him because that would never be possible, but to refocus my attention on something positive and to help save another little life. That turned out to be a very important part of my healing process.
Hugs to you!