Gosh I'm so sorry to hear that

It does suck when animals die! But remember that it isn't always your fault and there isn't always something you can do about it, even if you realize the animal has a problem (and I know it can be hard to tell!). Or maybe he was old.
At any rate, I would get a necropsy done on him, that way you can make sure he didn't die of anything your other animals might catch.
Zoe