Thanks everyone for the hugs! We are really doing ok now, it was hardest for my son but he's much better. He adored Sydney but now he feels more relieved that it's over and she doesn't hurt anymore. You know how it is when you know the end is coming sometime soon and you dread it more than anything.
They have another cat, but she totally ignored my son... then after Sydney was gone she came up to him and was rubbing up against him and giving him kisses. It's funny how they just know, and it made him feel so much better. He'll be gone 5 months in basic training and school but when he gets home in August he thinks he'll be ready to get a new kitty.