When my sweet Thelma passed away, I asked our vet what to do for her sister Louise. They said to be sure to give her extra loving and just keep an eye on her. She would come around. Louise did well but I think she got to say her goodbye because Thelma passed while I was at work. It was a surprise and very heartbreaking to me. It has been 1 1/2 years and I still miss her. I also think Louise did well because we had a smaller dog so he kept her busy.
I know cats are different from dogs...as we have 4 cats! I do hope your little Man gets through the loss without too much issues. Give him some extra snuggles tonight.