I lost my own beloved Amber a year and a half ago--in May of 2008--and I still cry sometimes when I think of her. And I think of her a LOT!! She gave me so much joy and comfort and I loved her so very much, just as you do your Bella.
Please realize that you DID make the right decision. Bella had an incurable illness and she was really beginning to suffer. No cat mom or dad wants their furchild to suffer needlessly, and it is a kindness to relieve them of their pain and suffering. It truly is the most unselfish act of love.
Love to you, and peace to your beautiful Bella.
Warm hugs,
Patti
How you behave towards cats here below determines your status in heaven.~~R.A. Heinlein