You have my sympathy: we lost two of our cats last year. Four Paws in August, and Georgie in the lead up to Christmas. Georgie was ~15.5 years old, and had been FIV-positive for at least 5 years. But that doesn't mean you did the wrong thing!
FIV is like HIV: having HIV does not necessarily mean you have
AIDS, but it does mean you're likely to develop it. We found that Georgie had FIV during a routine test, not because she was having a problem. Thereafter whenever there was any hint of an infection/whatever she was rushed off to the vets.
If White was having trouble with month-old wounds his FIV may have been much more advanced than Georgie's, and you probably did the right thing. Letting them go can be better than dragging them through more pain (that doesn't make you feel much better at the time though). And taking care of an FIV+ animal is a significant undertaking, both for you and for the cat. I readily accept that not everyone will go to the lengths we will...
Georgie was an adoptee (her previous owner moved to Darwin and left her behind at some flats we know someone in) and when she came to live with us she had a lot of trouble coming to terms with being shut in at night. It was ~6 years later that we found she had FIV: no idea how long she'd had it. At least after that she got to go out at night, because we enclosed the entire back yard (including areas such as the garage roof) with cat netting, and the back yard and the house became her entire world. She was protected from fights with other cats, and they were protected from her (it also curtailed her turtledove diet
). When we moved house last year we built a different but similar system, with the back yard open to the sky (no more blowing leaves off the top). In the end it was complications related to FIV that finished her off (cancer being one of them) but she led a very sheltered life.
My first cat Richie became insulin-dependent diabetic and eventually succumbed to perinephric psuedo-cysts (a kidney problem): we gave him his insulin injection twice a day (getting import permits and regularly shipping special insulin from the UK for him) testing his blood sugar levels, etc. It may have helped that I'm also insulin-dependent... He was another adoptee (his first owners [in Bendigo] moved away and left Richie and his sister behind: she didn't survive).
Four Paws was another Bendigo adoptee: her owners didn't bother getting her medical attention and because she had diarrohea/etc decided she could be an outside cat. When Jane's mum adopted her, Four Paws was diagnosed as hyper-thyroid and started on oral medication. Then when Jane's mum passed away she came to us, and got the radiotherapy which brought her thyroid under control. Eventually (years later) her kidneys started to fail (presumably stressed from those initial years of undiagnosed hyper-thyroidism).
In January we adopted Monty (I suppose it's debatable as to who adopted who). He'd been a stray in the area ever since we moved in last June, and had had some horrible wounds (but we hadn't been able to get near him to inspect them). This story sounds similar to yours. After months we managed to get his trust, and had to decide what we were going to do: he was having a hard life, he would have been hard on the local wildlife, etc. In the end we adopted him, and his world has shrunk to our house and yard. But in his first vet visit (when he got "fixed up" - we have a vet relative who uses the terrible phrase "got his pockets picked") one of the barrage of tests he got was for FIV. I really don't want to think what we would have done if he came back positive, but luckily (and amazingly!) he didn't. He does have some amazing chest scars though.
Again, you have our deepest sympathy for your pain!
And that's a beautiful portrait of White!
P.S. Monty seems to think he's in heaven!
Regular food, warm dry beds, and a decent garden to "own"... Turns out he was a year old: probably a Christmas 2004 present gone wrong.