I know how you feel. I cried for weeks when my Beta, Apollo, Died. Same for Nina and Roku, My neon tetras. But my cleaner snail (Still yet to be named) Is surviving really good. Hopefully he ends up living awhile.
You have to understand that small animals such as fishes , hamsters and such have very short lives. It's not your fault that he/she/it died. At least it knew that you loved it and cared for it, and now it is resting in peace, or probably swimming in a gigantic golden ocean , freely , without a care in the world. It will always watch over you <3.