Hi and welcome.
I know we're all discouraged from buying pets from pet shops, and I do understand why. However, what's going to happen to all the poor animals who are still making it into shops and markets if people don't buy them, look after them and give them a decent chance at life? PTS is my guess if the pet shop can't sell them.
Kitten and puppy farms need to be shut down to stop the major supply of these animals to shops in the first place.
My Lily and Poppy were both pet shop cats, and I've never regretted it for a second.
Bellatrix, you would be best to get puss checked at the vet, for his ear, his general health, worming, vaccinations etc....... His problem could be simply from ear mites, which I believe is fairly easy to treat, but you do need to get a definite diagnosis, as you don't want to treat puss for the wrong thing.
I've never had experience with ringworm and its such a shame you've had to experience this yourself. Hopefully you are over the worst of it.
Please keep in touch.