Rest in peace Orange Cat.
Ellie, I knew that Sherbie had lost a buddy but I didn't know the story. What a sad ending and I'm sure both you and Sherbie miss him terribly. It just isn't fair, especially when you were only trying to help him. But as you said, he is at Rainbow Bridge now and probably watches over sweet Sherbie. They look like they might have been littermates.
Hopefully another cat who needs a home and a companion will find their way to your property and can share Sherbie's fab new outdoor cat house with him.