Aww ariesrising, (((hugs))) you poor thing! You did the right thing for Spice of course, kidney problems are common in older cats; sometimes they fade away, sometimes they're in pain. Now she's at rest. Try not to feel guilt, there's nothing you could have done.
I think a
whole lot of people out there get it, understand how something being a part of your life for so long, growing up with you is important to you. Do a search on gc for the words rainbow bridge and you'll find a whole bunch of examples of just how it's not a trivial thing :-). And I'm sorry right now your friend isn't being a friend when it matters.
So, does it go away? In time. Like valkyrie and others said, it's a bereavement. Though not a human Spice was a part of your life and hopefully time will heal. Try to think not that she isn't but concentrate on that she was.
Here is a link to a poem (thank you GeekyPenguin) called the Rainbow Bridge which might help, at this time.
http://www.petloss.com/poems/maingrp/rainbowb.htm
- Richard