Honestly the best thing I could recommend to ya at this moment is just make his last moments on earth as comfortable as possible. It maybe sad to think about but you can always hold your head up high and be able to say that you atleast gave him a nice happy life. As they say "all good things must come to an end at some point". Just know that even if he can't show you love or appreciation like a dog or a cat can that he still loves and appreciates everything you have done for him.