I am truly sorry for the loss of your animal.
It is possible that your animal was simply a runt that had genetic problems to begin with. By comparison- my four month old veileds are nearly adult size.
see some pics of my hatchlings at 6 week and 9 weeks from pics taken of a group a couple of years ago here and compare size with yours at 4 months:
https://www.chameleonforums.com/veiled-chameleon-growth-chart-23892/index2.html#post1094360
Secondly- eye problem- this is where I disagree a bit with with current forum guidelines for babies. Instead I'll just leave you this thought about the topic from Bert Langerwerf (one of the best lizard breeders ever to walk the earth- pioneered much of what we know about lizard husbandry and was the first to breed superworms as lizard food). When the Langerwerf's found out my father was a veterinarian, they said "OH! Vets! When there is an eye infection veterinarians always say "The lizard has an infection!" And then they want to use antibiotics and treat the infection. They never want to ask why is there an infection in the first place." They explained that wild lizards eat insects that are loaded with carotinoids from eating green leaves all the time. Captive lizards don't get this usually, unless the insects are fed a very good diet. And sometimes vit a is necessary as well to prevent eye infections.
Sometimes (very often) a bit of vit a will clear up an eye infection within a few treatments, and regular appropriate use will prevent most infections of this sort. It isn't the same approach as the antibiotic. Both have their place. But the vitamin a keeps the body functioning as it should, to prevent and fight infection on it's own. Without it, the antibiotic may not even work anyway because it is inappropriately prescribed. I've been there done/that myself with veterinary treatment of chameleons with eye problems. Tried using no vit a, only beta carotene on some panthers to see if I could get away without vit a, had eye infections within several months. Got antibiotic ointment from a vet, did nothing over a couple of weeks. Stopped the antibiotic ointment, gave in to the probability that beta carotene was not being converted by the lizards into vit a, gave the panthers actual vit a from drops from a capsule, and within 5 days had no more eye infections.
I'm not saying for sure this is what happened with yours or that your vet was not giving appropriate treatment- I don't know, I wasn't there, but this is one that bugs me a lot- 1x per month with vit a in a multivitamin will not do much for a young rapidly growing chameleon. It will help for a few days, but then the vitamins are used up/passed from the lizard. So the rest of the month it will be deficient. In the past with tiny babies with eyes that closed- I found that misting them and getting their eyes open and then immediately feeding reptivite-dusted insects, and repeating this for 2 or 3 meals in a row, will usually bring them back to a healthy condition. I had to learn that bit the hard way many years ago before I learned to use a multivitamin a bit more often than 1x per month (been breeding veileds 23 years now).
My final thought is if your husband wants to try again, try to buy a chameleon that is a bit older/larger than the one you tried with this time. As they get larger, they do become easier to care for, and you are less likely to end up with a genetic runt on your hands, or an animal that had a bad start in life.
Don't feel guilty- you did the best you could with the knowledge you had, and because of the size of your animal, I'd say it is probable that he was a genetic runt probably doomed from the beginning...
