It's hard to deal with the death of a pet... I've had 12 rats pass away so far, and not a single day goes by without me thinking of each and every one of them.
I try to think about it this way -- if we weren't there to love the little guys, who would? If I hadn't been there for Mizune, or Suki, or Totoro, or any of them they would have been snake food. Despite living such short lives, I have decided to make them live the happiest lives they could possibly ever experience. When one passes on I will miss him/her every single day for the rest of my life, but it comforts me to know that in his short little life he was the happiest rat on this planet (or just about the happiest =P). After he passes on, and the time is right, it'll be time to get another new little baby rattie to love and spoil. And in return I will be loved by them all, and they will all know that they were lucky to have found me.
"Love them while they're here, and miss them when they're gone. When the time is right another will come along." is what someone told me after I had my first rat put to sleep. It's the one thing I've been telling myself ever since that day.