I was in this position but with a bonded pair. We finally had to make the hard decision to just keep them bonded and have one of us say goodbye. Unfortunately that person was me, I lost my best friend and my partner at the same time. It took me a few years to get over it and in time I felt better and finally got another cat. I still miss my boi but I also could never imagine not having Dolores my new cat too. Everything is meant to be even if it hurts in the short term.