Hey! All is not lost. Cats with FIV can live long and happy lives. You would have to keep his food and water separate from the other kitties’, and honestly it probably would be more practical to let him live somewhere else. But plenty of people WILL adopt an FIV-positive cat (my brother’s cat is FIV-positive and she’s adored!!!!). You have done an amazing thing for this kitty. I know it’s hard to say goodbye, but the little man will forever be better off because of what you have done for him.