Speak to your vet about possibly administering interferon. As far as I know the evidence for interferon to treat FIV is iffy at best but have had a positive experience myself.
Don’t forget that a lot of the symptoms that manifest (weepy eyes etc) are secondary and even if the interferon doesn’t help manage the FIV you might see positive effects on any secondary viral infections.
Depending on where you reside, interferon can be VERY expensive though. There might be a cheaper oral alternative but I’m only familiar with the injectable versions.
Hope this helps
Can’t quite remember the exact cost but because the vets had to special order it in they had to charge the whole vial rather than per dose as no one else was using it. Costs a couple of hundred pounds that lasted quite a few jabs. This was a few years ago in the UK. Not sure about the costs now.