*tears*
My cat died last year from surgery at a vets office. She was really sick and I was absolutely devistated. She seemed like yours.
It's amazing how some animals can be so close to humans, they feel like a part of you, a part of your family. A part of you dies with them.
I'm so sorry to hear this, I know how you feel. Take comfort in knowing he is in a much better place where there is no more pain and suffering, knowing that you'll see him again.
I suggest after a bit you get another kitten. Seeing them play and explore takes your mind off of things, though you'll never forget your friend.