In conclusion : You must be very careful when the cat is a carrier of a virus! You should be alert to the least sign of illness! There are cats who are asymptomatic viral carriers, who yet remain more fragile than other cats. The most important thing is to give your cat high quality food and if possible food supplements, either as a cure or continuously to protect and encourage his immune system.
Don’t be scared to tell your vet when you are worried, and if you have the least doubt regarding your cats health, insist on obtaining a clear and well-reasoned response! If you sense that your vet is unsympathetic, and doesn’t take your concerns into account, change to a different vet!
Each cat deserves to be looked after and treated correctly, and it’s up to you to decide when his time has come, as you are the one who knows your cat and his behaviour the best, and only you can tell when something’s up. Don’t forget that a FIV+ cat can live in good health for a long time despite his virus, if you take good care of him. And above all, I beg of you, don’t give up!