Awww....I am so sorry.
You must be feeling so very sad right now. I can understand how you'd also feel sad, guilty and stupid all at the same time. I don't think you're lame....losing a much loved pet can be very hard. This is especially so when the pet was a source of comfort or many years of happy memories.
Maybe you can save a little cat toy that Spice liked and put it up on a shelf somewhere? That way, every time you see it, you can think of all of the happy memories.
You know, my dog was 13 years old when he had to be put down last year (on February 16, 2003). I was living in England at the time and I wasn't even there to be with him for his last moments. My family went through some struggles over the years and I think our dog was the one "person" we could count on! He always knew how to make us feel better! It sounds like Spice cared about you too!
I hope, in time, you will feel less and less sad and instead you'll have more and more nice memories of her.
.....Kelly