My best friend had to put down her 19 year old kitty. He had been her best friend all those years - had a TON of personality, would carry on a conversation, and put her to bed every night. She came home after, and just couldn't imagine her life without him. The house was so quiet - and her comfort when she was lonely, or bored, or down was gone. I advised her to get busy - clean out that closet, play a computer game - work on her relationship with her husband to make her need kitty comfort less.
Sound familiar? It should. I hope this helps illustrate to the newly quit what losing your "best friend" feels like - and maybe what things to do to help move past it.
She didn't have any choice but to adjust. If you look at your quit in the same way, perhaps your success will be assured!
Nancy