OMG! I'm so sorry, Laura. He was such a special boy.
No, you did not kill him. Don't even think that! You did everything you could for him. If I remember right, Metacam is used with hydration because it tends to affect the kidneys. This is not generally an immediate affect, but something that can cause chronic problems over time or slow damage, etc. Like alcohol and the liver. To me, it sounds like he was having seizures which means something was seriously wrong. I know that organ failure can cause seizures, for example if his cancer was causing one of his vital organs to fail. If this is the case, nothing could have saved him, and you did your best to make his passing pain-free.
And I know what you're thinking, and no, I doubt that any other surgeries or treatments would have saved him. You did the very best you could, as did your vet. It's a hard truth, but I think you need to know it so you don't blame yourself. Sometimes bad things happen to good people.
:hug:
Binky free, Cooper. We'll all miss you.
:rainbow: